Serra Dos Carajas Research Articles

Description of a New Species ofAspidoras(Siluriformes, Callichthyidae) from the Serra dos Carajás, Lower Tocantins River Basin, Brazil

A new species of Aspidoras (Corydoradinae) is described from the Serra dos Carajas, lower Tocantins River basin, representing the northernmost record of the genus at the edge of the Brazilian Shield into the Amazon basin. Aspidoras gabrieli is easily distinguished from all congeners by having the rays and interradial membranes of the dorsal and pectoral fins entirely and densely pigmented, the inner bony margin of the pectoral spine expanded as a narrow laminar shelf with edge smooth or scarcely serrated; lateral-line canal posterior to the two anterior lateral-line ossicles absent (also in A. taurus), naked predorsal region (also in A. velites and A. psammatides), large brown oval spots on the flank and caudal peduncle that sometimes merge to form irregular patches (also in A. maculosus, A. albater, A. lakoi, and A. depinnai), and several additional morphometric distinguishing features. Comments on generic allocation and interspecific relationships are presented. Uma nova especie de Aspidoras (Corydoradi...

Morphological and compositional variations of zircon and their metallogenetic implications: the example of the Jamon, Serra dos Carajás and Velho Guilherme suites, Amazonian Craton

Zircon from granites of the Jamon (JS), Serra dos Carajas (SCS) and Velho Guilherme (VGS) suites were studied by SEM trough backscattered and cathodoluminescence images and EDS analyses. Granites and greisens of the VGS have zircons dominantly anhedral, altered and intensely corroded, enriched in Hf and with the lowest Zr/Hf ratios. In the granites, these ratios decrease towards the more evolved varieties. Zircons of the JS are euhedral to subhedral, zoned and little altered, comparatively depleted in Hf and displaying the highest Zr/Hf ratios, indicating limited potential for tin associated mineralization. Zircons from granites of the SCS are subhedral to anhedral, altered and corroded showing Hf contents and Zr/Hf ratios intermediate to those of the JS and VGS. The granites of the VGS with associated mineralization of Sn, Ta, and W contain zircons with Zr/Hf ratios varying from 7 to 22. It is concluded that ratios of that order can be used as a prospecting guide of specialized granites. On the other hand, zircons from the greisens associated with the Cigano Granite of the SCS have average Zr/Hf ratios around 23, but no cassiterite was found in these rocks. This indicates that those zircons preserved their magmatic geochemical signature. This study distinguished the three granitic suites in terms of zircon composition and demonstrated the importance of their geochemical signature, especially in terms of Zr/Hf ratio, in the identification of specialized granites. EDS-SEM analysis can thus be used in a preliminary assessment of the metallogenic potential of tin granites.

Petrography, magnetic susceptibility and geochemistry of the Rio Branco Granite, Carajás Province, southeast of Pará, Brazil

The Paleoproterozoic Rio Branco stock intrudes the RESUMO: Petrografia, suscetibilidade magnetica e geoquimica do Archean Cruzadao biotite monzogranite. It occurs west of the Canaa dos Carajas city, close to the Sossego copper mine in the Carajas Prov- ince. It is constituted by undeformed and isotropic, hololeucocratic syenogranites, showing equigranular texture. The granite is formed essentially by perthitic alkali feldspar, quartz, and plagioclase, with additional variable amounts of chloritized biotite. Fluorite, allanite, and zircon are common accessory minerals, whereas pyrite and chal- copyrite are scarces. Albitization and subordinate greisenization are the main alteration processes that affected the granite. The secondary mineralogy is represented by albite, fluorite, topaz, chlorite, musco- vite, siderophyllite, and iron oxides. Magnetic susceptibility values are systematically low and vary between 1.3 x 10 -5 a 6.9 x 10 -4 (SI). The Rio Branco Granite is metaluminous to peraluminous and shows high FeOt/(FeOt + MgO). It has geochemical affinities with ferroan, reduced A2-subtype granites. The rare earth element (REE) patterns are flat with little heavy REE fractionation and show accentuated negative Eu anomalies (Eu/Eu* = 0.08 – 0.13). These characteristics are typical of evolved granites, derived from volatile-enriched liq- uids responsible by the intense subsolidus hydrothermal alteration. The dating of the Rio Branco granite did not give conclusive results, but the obtained data, associated with geological evidence, suggest that it is of Paleoproterozoic age. The comparison between the Rio Bran- co granite and Paleoproterozoic A-type suites of the Carajas Province suggests that the Rio Branco granite has more affinity with the Velho Guilherme suite and, in lesser degree, with the Serra dos Carajas suite. On the other hand, is clearly different from oxidized A-type granites of the Jamon suite. Despite its similarities with tin-specialized gran- ites, the Rio Branco Granite is not associated with tin mineralizations.

Two New Species ofBorreria(Rubiaceae) from Brazil, with New Distributional Records for Pará State and a Key to Species with Transversally Sulcate Seeds

Two new species of the genus Borreria, B. carajasensis E.L. Cabral & L.M. Miguel and B. elaiosulcata E.L. Cabral & L.M. Miguel, are described and illustrated, based on material collected from iron outcrops in the Serra dos Carajas region, Para State, Brazil. A key to morphologically similar species is provided; these species can be recognized by their transversally sulcate seeds. Borreria cupularis and B. multiflora are reported for the first time from the Para State.

Geologia, Petrografi a e Geoquímica do Batólito Seringa, Província Carajás, SSE do Pará

The Seringa Granite, with 2250 km² of outcropping area represents the biggest granite batholith of the Carajas Province. It is intrusive in Archean units of the Rio Maria Granite-Greenstone Terrane, located in the southeastern of the Amazonian Craton. The Seringa Granite is formed by two great petrographic groups: A) monzogranite rocks, represented by biotite-amphibole coarse-grained monzogranite, amphibolebiotite coarse-grained monzogranite; B) syenogranite rocks, represented by, porphyry amphibole-biotite syenogranite, heterogranular leuco-syenogranite, leuco-microsyenogranite, and heterogranular amphibolebiotite syenogranite. Biotite and amphibole are the varietal minerals and zircon, apatite, opaque, and allanite the accessories minerals. The Seringa Granite is subalkaline, metaluminous to peraluminous, display K2O/ Na2O ratios between 1 and 2 and FeOt/(FeOt +MgO) between 0.86 and 0.97. The patterns of REE show increase in negative europium anomalies from the less evolved facies to the more evolved facies. In these sense, it is enriched in light REE parallel to the impoverishment of heavy REE. It shows geochemical affinities with within-plate ferroan granites, of the A2-subtype and oxidized A-type granites. The fi eld relations and the petrographic and geochemical features of the Seringa Granite are not consistent with the evolution of its facies from a single magma pulse by fractional crystallization. The Seringa Granite show petrographic, geochemical and magnetic susceptibility properties that suggest its inclusion in the Serra dos Carajas Suite.

Fauna flebotomínica da Serra dos Carajás, Estado do Pará, Brasil, e sua possível implicação na transmissão da leishmaniose tegumentar americana

Serra dos Carajas, located in the southeast of Para State, Brazil, is a rich tropical forest where species of Leishmania sp. of medical interest are found, such as Leishmania (V.) braziliensis, L. (V.) lainsoni, L. (V.) shawi and L. (L.) amazonensis. They are transmitted by the following phlebotomi: Psychodopygus complexus or Ps. wellcomei, Lutzomyia ubiquitalis, Lu. whitmani and Lu. flaviscutellata. Considering the increase of immigrants in the region of the Carajas project, this study aimed to assess the Phlebotominae fauna and their possible participation in the transmission of American cutaneous leishmaniasis (ACL). The phlebotomi were captured from December 2005 to September 2007 at the following locations: i) Parauapebas Botanical Park; ii) an environmental protection area; and iii) Tapirape-Aquiri National Forest. During the 172 days of collection, 10 CDC (18 h to 6 h) and 2 Shannon (18 h to 20 h) light traps were used. Of the 22,095 phlebotomi captured, 6,789 (31%) were male and 15,306 (69%) were female, and they belonged to 69 species and three genera, including Psychodopygus, Lutzomyia and Brumptomyia. A total of 19 (0.16%) natural infections of the following species were detected: Ps. davisi (4), Ps. h. hirsutus (3), Lu. umbratilis (3), Lu. richardward (2), Lu. brachipyga (2), Lu. ubiquitalis (2), Lu. trinidadensis (1) and Lu. migonei (1). Although no infection was found in Ps. wellcomei/complexus, the main vector of L. (V.) braziliensis in the region, this species was the most prevalent (16%), followed by Ps. davisi (15.4%), Ps. carrerai (4.2%), Lu. shawi (3.9%), Lu. brachipyga (2.5%) and Lu. richardward (1.2%). These results show the importance of these phlebotomi as possible vectors of ACL in Serra dos Carajas.

GEOLOGY, GEOCHEMISTRY AND MAGMATIC EVOLUTION OF THE PALEOPROTEROZOIC, ANOROGENIC OXIDIZED A-TYPE REDENCAO GRANITE OF THE JAMON SUITE, EASTERN AMAZONIAN CRATON, BRAZIL

The anorogenic oxidized A-type Redencao granite, of Paleoproterozoic age, is located in the Amazonian craton to the south of the Serra dos Carajas, in Brazil. The granitic pluton is comprised essentially of monzogranites disposed in near-concentric zones. Except for clinopyroxene-bearing monzogranites generated by accumulation of mafic minerals, the least-evolved facies is a coarse biotite–hornblende monzogranite that evolved by fractional crystallization to the dominant facies, a coarse (hornblende) –biotite monzogranite. The central portion of the pluton consists of leucogranites, which were probably derived from an independent magma. Seriate and porphyritic biotite monzogranite varieties cross-cut the coarse (hornblende)–biotite monzogranite, forming annular structures. The porphyritic monzogranites are at least in part generated by mingling between the magmas of the coarse biotite monzogranite and leucogranites. The mixing of magmas is probably more common in granitic plutons than generally admitted. The different varieties of the Redencao pluton are ferroan alkali-calcic A-type granites [FeO t /(FeO t + MgO) values of 0.83 to 0.94; K 2 O/Na 2 O 1 to 2]. The oxidized character of the Redencao pluton is revealed by the ubiquitous occurrence of magnetite and titanite, and relatively lower FeO t /(FeO t + MgO) values and higher magnetic susceptibility compared to those observed in typical reduced A-type granites.

Processamento e integração de imagens multiespectrais, de radar e aerogeofísicas do bloco serra leste (Carajás, PA) e discussão do potencial para mineralização de ferro

Este trabalho utilizou dados multiespectrais (ETM+/Landsat 7), de radar de abertura sintética (RADARSAT-1 e MAPSAR simulado) e aerogeofísicos para caracterização geológica e geração de alvos exploratórios para mineralizações de ferro no bloco Serra Leste, porção oriental da Serra de Carajás (PA). A técnica Minimun Noise Fraction (MNF) foi aplicada às seis bandas do sensor ETM+/Landsat 7, produzindo-se o realce de coberturas ricas em ferro. Dados SAR permitiram a observação da macrotopografia e lineamentos que foram também interpretados com base em dados aerogeofísicos e multiespectrais. As imagens geofísicas e SAR do RADARSAT-1 foram integradas por meio da técnica IHS (intensidade-matiz-saturação), e os produtos gerados foram usados para uma melhor delimitação de unidades geológicas e para definição de alvos para prospecção de ferro. O método de classificação supervisionada Spectral Angle Mapper (SAM) foi aplicado a um conjunto de imagens geofísicas selecionadas a partir da determinação do modelo descritivo das mineralizações de ferro e das assinaturas geofísicas verificadas no alvo Serra Leste. Utilizando-se a ocorrência documentada de ferro na região como ponto de treinamento, um mapa de favorabilidade foi produzido. Os resultados da classificação SAM mostraram-se equivalentes ou superiores quanto a sua acurácia quando comparados ao mapa geológico e produtos de realce espectral produzidos neste artigo.

Musgos (Bryophyta) da Serra dos Carajás, estado do Pará, Brasil

In the Serra dos Carajas a mineral province situated in the south Para state, where occur a big quantity of ore as iron, manganes, cooper, gold, nikel and others, were carried collection of bryophytas (mosses), to aim of inventory the bryoflora the Serra in its different ecossystems, and to test the hypothesis that for each ecossistem, correspond determined specific diversity of the mosses. There were identified 87 species, 3 varieties and 20 families. To each species are included data of the material examined and comments about the principal morphological characteristics. Sematophyllum subsimplex (Hedw.) Mitt., Pilosium chlorophylum (Hornsch.) Mull. Hal., Calicostella pallida (Hornsch.) Angstr. and Campylopus savannarum (Mull. Hal.) Mitt. stand out by abundance. The three first were found in all ecossistem studied. Fourteen species were considered rare due have been colected only one time. Leucomium steerei B.H. Allen & Veling and Fissidens weiri var. hemicraspedophylus Mitt. are new occurences to Brazilian Amazon and to Para state. Phyllodon truncatulum (Mull. Hal.) W.R. Buck, Lepidopilum polytrichoides (Hedw.) Brid. and Groutiella tumidula (Mitt.) Vitt are new occurrences only to Para state. The specific diversity of the Serra dos Carajas compared the others locals were considered high.

ALTERAÇÃO HIDROTERMAL DAS ROCHAS MÁFICAS DO ALVO ESTRELA (Cu-Au), SERRA DOS CARAJÁS, PARÁ

The host rocks of the Estrela Cu-Au deposit in the Serra dos Carajas region are andesites and gabbros of the Grao Para Group, of the Itacaiunas Supergroup, formed at 2.7 Ga. The deposit is in a 400-600 m thick sequence ofaltered andesites and gabbros still presenting relict ophitic to subophitic-type igneous textures. The gabbros and andesites are possibly related to magmatic are origin, as suggested by Se/Ti ratios of 0.02-2.28 x 10 -3 for the gabbros and 3.25 x 10 -3 _ 1.67 X 10 -3 for the andesites. The andesites present higher REE content (LREE = 90.50 a 471.67 ppm) than the gabbros (LREE = 43.76 a 230.57 ppm), what may reflect the original igneous content or an advanced alteration stage. The host roeks of the Estrela Cu-Au Deposit have been affected by an early calcic-sodie alteration followed by a potassic alteration, accompanied by ferrifieation and sulfidation, which transformed the igneous protoliths into biotite-rich rocks. The early calcic-sodic alteration is represented by hastingsite, Fe-pargasite, Fe-homblende, oligoclase-andesine, albite, quartz, magnetite and minor Fe-biotite, Fe-epidote and chlorite. The potassic alteration overprinted the calcic-sodic mineral assemblage and is characterized by siderophyllite, biotite, Fe-epidote, fluorite, radioactive minerais, quartz, chamosite, dravite, schorlite, magnetite, chalcopyrite, pyrite, pyrrhotite, molybdenite and minor bornite. The late alteration stage is a greisenization developed at localized sites mainly in the andesites. The greisen mineralogy is quartz, zinwaldite, Li-muscovite, dravite-schorlite, fluorite, topaz, titanite, F-apatite and chlorite. Calcite, chamosite, topaz, quartz and tourmaline veins post date the mineralization and greisenization. This alteration sequence suggests that the hotter fluids, assoeiated with the potassic alteration and albitization were oxidizing alkaline and held high K and CI activities in addition to high Na:Ca ratios. During the cooling path a deereasing in the Na:Ca ratio probably occurred accompanied by a sharp increasing of F activity, as evidenced by the massive presence of fluorite. During the greisenization stage the fluids became reducing and aeidic permitting the stabilization of the Li-muscovites and the other greisen mineral assemblages.

Novas ocorrências de hepáticas (Marchantiophyta) para o estado do Pará, Brasil

Durante o inventário das hepáticas da Serra dos Carajás, foram identificadas quatro novas ocorrências para o estado do Pará: Frullania beyrichiana (Lehm. & Lindenb.) Lehm. & Lindenb, Frullania kunzei (Lehm. & Lindenb.) Lehm. & Lindenb, Symphyogyna aspera Steph. e Lophocolea leptantha (Hook. & Tayl.) Tayl. Esta última espécie, antes somente relacionada para as regiões Sudeste e Sul do Brasil, é nova ocorrência para o eixo Norte-Nordeste brasileiro. Cada espécie é acompanhada de comentários morfológicos, taxonômicos e ecológicos.

The Serra Pelada Au-PGE deposit, Serra dos Carajás (Pará State, Brazil): geological and geochemical indications for a composite mineralising process

The Serra Pelada Au-PGE-rich deposit is located in the Serra dos Carajas, a leading mining area in Brazil. This region is characterised by a complex geological and structural framework and is affected by deep lateritisation which has lasted for more than 70 Ma. The Serra Pelada deposit is emplaced in a late-Archean low-grade metasedimentary sequence (Rio Fresco/Aguas Claras Formation) which is host to other gold deposits in the region (Igarape Bahia, Aguas Claras). The Rio Fresco/Aguas Claras sequence was deposited in tectonic basins developed on Archean basement and Au-bearing greenstone terranes which were intruded by PGE-rich layered mafic complexes (e.g. Luanga). The Serra Pelada mineralisation is located along a regional, complex system of strike-slip faults (Cinzento-Carajas systems) which were active during the late Archean to early Proterozoic. The mineralisation appears to be concentrated along a faulted hinge zone of a fold. Ore zone rock facies are dominated by low-grade ferruginous to carbonaceous metasiltstones and minor sandstones, locally brecciated and cemented by quartz (±sulphide) stockwork. Supergene alteration led to partial to total transformation into friable aggregates of kaolinite, Fe oxide-hydroxides, silica and secondary phosphate-sulphates even at depths exceeding 200 m. Precious metals are exceptionally enriched, with up to more than 1,000 ppm Au+PGE in some peculiar ferruginous-graphitic zones locally called "hidrotermalito". Geochemistry shows complex patterns of major and trace elements, particularly rare-earth elements (REE), in mineralised vs. nonmineralised samples. These patterns are interpreted in terms of variable degree of superposition of hydrothermal and supergene alteration. Precious metals show progressive increase from samples with hydrothermal imprint to samples with supergene imprint. The geological evolution of the Carajas region and the characteristics of mineralisation at Serra Pelada may suggest a composite mineralising process: hydrothermal activity (by fluids likely originated from granitoids) was followed by supergene alteration during long-lasting lateritisation to develop extreme precious metal enrichments in a geological context probably already anomalous for Au and PGE.

Taxonomic Revision of the South American Subspecies of the Turtle Kinosternon scorpioides

Taxonomic Revision of the South American Subspecies of the Turtle Kinosternon scorpioides

ASPECTOS ECOLÓGICOS DA VEGETAÇÃO RUPESTRE DA SERRA DOS CARAJÁS, ESTADO DO PARÁ, BRASIL

São fornecidos aspectos ecológicos gerais da vegetação "rupestre" da Serra dos Carajás, envolvendo informações sobre composição floristica, associação solo/planta, fauna/planta e distribuição geográfica das espécies. Nesta vegetação foi registrado um total de 232 espécies, a maioria ervas, distribuídas em 145 gêneros e 58 famílias botânicas. As duas famílias mais bem representadas foram Gramineae e Leguminosae, seguidas de Cyperaceae, Myrtaceae, Rubiaceae, Malpighiaceae, Euphorbiaceae e Compositae. Algumas famílias apresentam espécies arbóreas esporadicamente representadas em "capões de árvores" ou isoladas como Anacardiaceae, Rutaceae, Sapotaceae e Vochysiaceae. Há famílias de ocorrência restrita em locais onde há acumulo de água, como Begoniaceae, Burmaniaceae, Eriocaulaceae, Gentíanaceae, etc. E finalmente aquelas famílias de ocorrência apenas ocasional, como Acanthaceae, Annonaceae. Chrysobalanaceae, Palmae, Sterculiaceae, etc. Parece que os polinizadores mais comumente encontrados na vegetação rupestre são as abelhas. Há também outros animais ali associados à biologia das plantas como meliponídeos, tabanídeos, répteis e pássaros. Além de apresentar uma insignificante camada lodosa, associada a musgos e líquens o solo onde se assenta a vegetação "rupestre" apresenta uma grande quantidade de ninhos de cupins, na transição entre as estações seca e chuvosa. A necessidade de preservação da área estudada justifica-se pela presença de inúmeras espécies endêmicas (ex. Ipomoea cavalcanteiAustin), espécies novas para a ciência (ex. Erytroxylum nelson-rosaePlowman), espécies medicinais (ex. Pilocarpus micmphylusStapf. ex. Wardleworth) e espécies ornamentais (ex. Vellozia glochideaPohl), todas associadas a uma fauna e a um tipo de solo que ainda carecem de pesquisas mais aprofundadas para melhor conhecê-los.

DEFORMAÇÃO DE ROCHAS GRANITÓIDES EM REGIME DÚCTIL: O EXEMPLO DO GNAISSE ESTRELA, REGIÃO DE CARAJÁS

The Estrela Gneiss is an Archaean gneiss-granitic body that outcrops to the east of the Serra dos Carajas. Detailed microscopic studies of these gneisses and deformed pegmatoid rocks revealed several microstructures in grains of quartz, feldspars and mafic minerals, indicating plastic flow during deformation. The microstructural features appear firstly in quartz, afterwards they are observed in K-feldspars and finally in plagioclase. The evolution of these microstructures follows the sequence: 1. wavy extinction; 2. kink bands; 3. sub-grains; 4. new grains; 5. wavy extinction in new grains; and 6. cyclic recrystallization. During the stages 1 and 2 recovery mechanisms are more important, however, when dynamic recrystallization is present, mechanisms of sub-grain rotation and grain boundary migration start to act. The interaction of these processes account for a global plastic behavior and the rheological contrasts between quartz and feldspars become negligible. The ductile behavior of feldspars suggests that shear zones developed under temperatures higher than 500°C.

A New Species of Daphnopsis (Thymelaeaceae) from Brazil

Daphnopsis filipedunculata, a new species from Serra dos Carajas, Para, Brazil, is distinguished by its long, thin primary peduncles and constricted hypanthium.

Characterization of Hydrological and Hydrochemical Cycles as a Tool for Evaluation of Environmental Impact of Mining in Serra Dos Carajas, Amazonia, Brazil

The objective of this work is to show the importance of knowing, in detail, the hydrological and hydrochemical cycles so as to define the dynamic conditions for an ecosystem equilibrium and to detect the modifications introduced by open-cast mining, which is a potential cause of environmental impact. Over four years research was carried out in the Carajas area to evaluate the elimate, soil and water characteristics. About the five hundred and fifty water samples from rivers, lakes and “igarapé” were collected and analysed from forty different points of the area. At nine different points, two hundred sixteen soil samples were collected and analysed. The analysed results were assembled with pluviometry, humidity, potential evaporation, insolation and temperature data for the area. The data reveal that residence time of water is short in all “stages” of the cycles (convective rain); the pH is acidic (between 4.5 and 6.0) with high values of free CO2 (average 30 ppm) and saturated in dissolved O2 (average 8.O ppm) which produces a high degree of water reactivity when in contact with the surface. The Carajas ecosystem is in dynamic equilibrium with these conditions. The water percolation through tailings from iron and manganese mining produces an agent that dissolves and removes mineral particles that in run off arrives in surface and groundwater, changing its physical-chemical equilibrium and disturbs the aquatic biota. At the start of exploration were detected Cr 0.14 ppm, Mn 0.43ppm, Pb 0.20 ppm and Ni 0.04ppm. Salobo polymetals deposit has a very complex mineral paragenesis with Cu, pb, Ag, Mo, Co, Zn and other metals such as sulfide. This deposit has a high pollution potential since its tailings will will be exposed in the open.

Thermal biology and flight distance ofTropidurus oreadicus(Sauria Iguanidae) in an area of Amazonian Brazil

The thermal biology and flight distance of the tropical lizard Tropidurus oreadicus was studied on iron ore outcrops (called canga) at Serra dos Carajas, in Brazilian Amazonia. Body temperature varied markedly throughout the day (range 32.0 to 38.1 °C), but mean preferred body temperature was 35.8 °C. The air temperature in the microhabitat explained a considerable part of Tropidurus oreadicus body temperature variation, but other factors such as direct insolation and substratum teperature may also be of importance. In the morning, lizards usually climbed onto rocks and assumed progressively changing body orientations and inclinations which increased the interception of sunlight. Later they retreated to vegetation. This suggested that the importance of rocks as basking sites changes during the morning due to the angle of the sun. The flight distance was greater when body temperature was low and this may be of survival value in open areas such as the mineral outcrops of Serra dos Carajas.

Criptomelana cuprífera formada durante o intemperismo das rochas da jazida de cobre do Salobo 3α, Serra dos Carajás

Estudos geoquímicos e mineralógicos do manto de alteração intempérica sobre rochas mineralizadas em cobre do Salobo 3α Serra dos Carajás, mostraram que o cobre liberado dos sulfetos por dissolução é, em grande parte, fixado no perfil de intemperismo e localizado em três principais fases mineralógicas: fase silicatada, fase ferruginosa e fase manganesífera. Apenas a fase manganesífera é objeto deste estudo. Trata-se de uma fase monominerálica, identificada como criptomelana, do grupo da hollandita, com teores variáveis de potássio. Diferentes técnicas analíticas (difração de raios-X, espectrometria infravermelho e microssonda eletrônica) foram utilizadas para caracterizar esta criptomelana e mostrar que ela pode conter até mais de 20% de Cu0.

Tipos de vegetação metalófila em áreas da serra de Carajás e de Minas Gerais, Brasil

Em áreas da Serra de Carajás, Pará, e em áreas da Cadeia do Espinhaço, Minas Gerais, Brasil, foram coletadas plantas e nelas analisadas as concentrações de Cu, Pb, Ni, Cd, Cr, Co, Mn e Fe. Os resultados indicam que as plantas das áreas de Carajás concentram Cu, Pb, Ni, Cr e Fe acima da normalidade e que as plantas das áreas da Cadeia do Espinhaço concentram Ni, Mn, Cu, Pb, Cd e também Fe. Com base nestes resultados e nos aspectos fisionômicos da vegetação, podemos supor a existência de diferentes tipos de vegetação metalófila nestas áreas, as quais podem pertencer a uma única provir ia biogeoquímica (Carajás - Espinhaço), rica em ferro e outros metais pesados.