Artur Cezar Bastos Neto

Rare earth element and yttrium geochemistry applied to the genetic study of cryolite ore at the Pitinga Mine (Amazon, Brazil)

ABSTRACT This work aims at the geochemical study of Pitinga cryolite mineralization through REE and Y analyses in dissem-inated and massive cryolite ore deposits, as well as in fluorite occurrences. REE signatures in fluorite and cryoliteare similar to those in the Madeira albite granite. The highest 6REE values are found in magmatic cryolite (677 to1345 ppm); 6REE is lower in massive cryolite. Average values for the different cryolite types are 10.3 ppm, 6.66 ppmand 8.38 ppm (for nucleated, caramel and white types, respectively). Disseminated fluorite displays higher6REE val-ues(1708and1526ppm)thanfluoriteinlateveins(34.81ppm). Yttriumconcentrationishigherindisseminatedfluoriteand in magmatic cryolite. The evolution of several parameters (REE total , LREE/HREE, Y) was followed throughoutsuccessive stages of evolution in albite granites and associated mineralization. At the end of the process, late cryolitewas formed with low REE total content. REE data indicate that the MCD was formed by, and the disseminated oreenriched by (additional formation of hydrothermal disseminated cryolite), hydrothermal fluids, residual from albitegranite. The presence of tetrads is poorly defined, although nucleated, caramel and white cryolite types show evidencefor tetrad effect.

Paleoproterozoic (~1.88Ga) felsic volcanism of the Iricoumé Group in the Pitinga Mining District area, Amazonian Craton, Brazil: insights in ancient volcanic processes from field and petrologic data

O Grupo Iricoume corresponde ao mais expressivo vulcanismo Paleoproterozoico do Escudo das Guianas, craton Amazonico. As rochas vulcânicas sao coexistentes com os granitoides Mapuera, e pertencem ao magmatismo Uatuma. Possuem idades U-Pb em torno 1888 Ma, e assinaturas geoquimicas de magmas tipo-A. As vulcânicas do Iricoume consistem de traquitos a riolitos porfiriticos, associados a ignimbritos ricos em cristal e tufos co-ignimbriticos de queda e surge. A quantidade e a morfologia dos fenocristais podem ser utilizadas para distinguir lava (fluxo e domo) de unidades hipabissais. A morfologia dos cristais em ignimbritos permite a distincao entre unidades efusivas e ignimbritos, quando os piroclastos estao obliterados. Tufos co-ignimbriticos sao macicos e alguns exibem estratificacoes que sugerem deposicao por correntes de tracao. Temperaturas de cristalizacao de zircao e apatita variam de 799°C a 980°C, sao compativeis com temperaturas de liquidos tipo-A e podem ser interpretadas como temperatura liquidus minima. Estimativas de viscosidade para composicoes rioliticas e traquiticas fornecem valores proximos a de liquidos determinadas experimentalmente e ilustram curvas tipicas de decaimento exponencial, com a adicao de agua. O posicionamento das vulcânicas Iricoume e de parte dos granitoides Mapuera foi controlado por falhas anelares em ambiente intracratonico. Uma genese relacionada a ambiente de complexo de caldeiras pode ser assumida para a associacao vulcano-plutonica Iricoume-Mapuera no Distrito Mineiro de Pitinga.

Regional Assessment of Sewage Contamination in Sediments of the Iguaçu and the Barigui Rivers (Curitiba City, Paraná, Southern Brazil) using Fecal Steroids

Steroids derived from fecal (coprostanol, epicoprostanol and coprostanone) and mixed (cholesterol, cholestanol and cholestanone) sources were analyzed in 19 surface sediments collected in two samplings by gas chromatography with flame ionization detection (GC/FID) in order to provide a regional assessment of the sewage contamination in the Iguacu and Barigui Rivers, Southern Brazil. The mean concentrations of coprostanol in the Summer (109 ± 122 mg g-1) and Winter (130 ± 116 µg g-1) seasons in 2007, with maximum value of approximately 330 mg g-1, situate the studied sediments as heavily contaminated by sewage. Diagnostic ratios among selected compounds suggested that domestic effluents were the main source of contamination, although the contribution of manure from livestock might also be locally important. The results show that the release of raw sewage may pose a relevant threat to the environmental health of river systems when the capacity to disperse and dilute the effluents is reduced during periods of small river water flow.

Waimirite-(Y), orthorhombic YF3, a new mineral from the Pitinga mine, Presidente Figueiredo, Amazonas, Brazil and from Jabal Tawlah, Saudi Arabia: description and crystal structure

Abstract Waimirite-(Y) (IMA 2013-108), orthorhombic YF3, occurs associated with halloysite, in hydrothermal veins (up to 30 mm thick) cross-cutting the albite-enriched facies of the A-type Madeira granite (~1820 Ma), at the Pitinga mine, Presidente Figueiredo Co., Amazonas State, Brazil. Minerals in the granite are ‘K-feldspar’, albite, quartz, riebeckite, ‘biotite’, muscovite, cryolite, zircon, polylithionite, cassiterite, pyrochlore-group minerals, ‘columbite’, thorite, native lead, hematite, galena, fluorite, xenotime-(Y), gagarinite-(Y), fluocerite-(Ce), genthelvite–helvite, topaz, ‘illite’, kaolinite and ‘chlorite’. The mineral occurs as massive aggregates of platy crystals up to ~1 μm in size. Forms are not determined, but synthetic YF3 displays pinacoids, prisms and bipyramids. Colour: pale pink. Streak: white. Lustre: non-metallic. Transparent to translucent. Density (calc.) = 5.586 g/cm3 using the empirical formula. Waimirite-(Y) is biaxial, mean n = 1.54-1.56. The chemical composition is (average of 24 wavelength dispersive spectroscopy mode electron microprobe analyses, O calculated for charge balance): F 29.27, Ca 0.83, Y 37.25, La 0.19, Ce 0.30, Pr 0.15, Nd 0.65, Sm 0.74, Gd 1.86, Tb 0.78, Dy 8.06, Ho 1.85, Er 6.38, Tm 1.00, Yb 5.52, Lu 0.65, O (2.05), total (97.53) wt.%. The empirical formula (based on 1 cation) is (Y0.69Dy0.08Er0.06Yb0.05Ca0.03Gd0.02Ho0.02Nd0.01Sm0.01Tb0.01Tm0.01Lu0.01)∑1.00[F2.54⃞0.25O0.21]∑3.00. Orthorhombic, Pnma, a = 6.386(1), b = 6.877(1), c = 4.401(1) Å, V = 193.28(7) Å3, Z = 4 (powder data). Powder X-ray diffraction (XRD) data [d in Å (I) (hkl)]: 3.707 (26) (011), 3.623 (78) (101), 3.438 (99) (020), 3.205 (100) (111), 2.894 (59) (210), 1.937 (33) (131), 1.916 (24) (301), 1.862 (27) (230). The name is for the Waimiri-Atroari Indian people of Roraima and Amazonas. A second occurrence of waimirite-(Y) is described from the hydrothermally altered quartz-rich microgranite at Jabal Tawlah, Saudi Arabia. Electron microprobe analyses gave the empirical formula (Y0.79Dy0.08Er0.05Gd0.03Ho0.02Tb0.01 Tm0.01Yb0.01)∑1.00[F2.85O0.08⃞0.07]∑3.00. The crystal structure was determined with a single crystal from Saudi Arabia. Unit-cell parameters refined from single-crystal XRD data are a = 6.38270(12), b = 6.86727(12), c = 4.39168(8) Å, V = 192.495(6) Å3, Z = 4. The refinement converged to R1 = 0.0173 and wR2 = 0.0388 for 193 independent reflections. Waimirite-(Y) is isomorphous with synthetic SmF3, HoF3 and YbF3. The Y atom forms a 9-coordinated YF9 tricapped trigonal prism in the crystal structure. The substitution of Y for Dy, as well as for other lanthanoids, causes no notable deviations in the crystallographic values, such as unit-cell parameters and interatomic distances, from those of pure YF3.

Caracterização Petrográfica e Geoquímica da Parte Leste do Granito Europa, Distrito Mineiro de Pitinga, AM

The important mineral deposits of the Pitinga Mine, in the Amazonian region are related to A-type granites intruded in the Iricoume Group. The Europa granite is one of these A-type rocks, intruded in the Iricoume Group, which is represented by subaerial vulcanoclastic rocks (crystal-rich ignimbrites, thin massive tuffs and siltic tufaceous arenites) and minor hipabissal rhyolites. The volcanic rocks were probably generated in a caldera environment. The Europa granite is an alkali-feldspar peralkaline granite (hipersolvus) without genetic relationship with to the volcanic rocks of the Iricoume Group, but it could have been generated during the resurgence stages. The petrographic and geochemical data attest that fractional crystallization process was the principal mechanism during the crystallization, which led to the generation of two different granitic facies. The Nb soil anomalies overprinted on the more differentiated facies are related to the astrophillite weathering.

Aplicação de técnicas de sensoriamento remoto na investigação do controle do posicionamento do Complexo Carbonatítico Seis Lagos e no estudo do depósito (Nb) laterítico associado (Amazonas, Brasil)

The main goals of this study were to identify geological structures that controlled the emplacement of the Seis Lagos Carbonatite Complex and contribute to the knowledge of the associated deposit, through the delimitation of the lateritic crust, the identification of internal structures and hydrothermal zones, where higher concentrations of Nb and REE may occur. Geophysical techniques, analysis of digital terrain elevation and processing techniques of orbital data were employed. The main regional structure has E-W direction and length of about 400 km. The positioning of the SLCC occurred where it is intersected by structures trending NE-SW and NW-SE. The boundaries of the lateritic crust are largely rectilinear, suggesting brittle structures, that may be the walls of the magma conduct, following open faults and fractures, or faults that affect the body after its crystallization. The main structures affecting the deposit have EW or NNW-SSE direction, controlled the formation of valleys and ridges, and karst processes with basin formation; therefore exerted role during laterization. Clayey zones likely related to hydrothermal processes were identified in four structures.

Evaluation of biological absorption coefficient of trace elements in plants from the pitinga mine district, amazonian region

Specimens of Ampelozizyphus amazonicus and Adiantum sp., together with adjacent soils, were sampled in the Pitinga Mine District, Amazonian region, in order to investigate the distribution of some trace elements in plants and soils, and their relation to the presence of mineral deposits. The Pitinga Mine contains large deposits of tin, with high concentrations of niobium and zirconium, hosted by the Madeira Granite, which is intrusive into a volcanic sequence named the Iricoume group, all of them with Paleoproterozoic age. Our results point to the potential use, for both plants, of the Biological Absorption Coefficient (BAC) as an indicator of mineral deposits when the elements involved in this process have moderate to high mobility in the supergene environment. The high BAC for gold indicates that this element can be used as an indicator of gold deposits. The presence of sulfide deposits is indicated by high BAC for Cu, Zn and Pb, whereas tin deposits are indicated by increasing BAC for Y and Sn. This suggests that the BAC of some trace elements in both plants is a good indicator of geochemical enrichment associated with mineral deposits. The importance of biogeochemistry for mineral exploration is confirmed for areas with thick vegetal cover.

Variações mineralógicas e petrográficas na porção central do albita-granito Madeira, Pitinga, AM

O albita-granito de Pitinga e uma facies porfiritica do granito paleoproterozoico Madeira (~1,83Ga) que contem concentracoes importantes de criolita disseminada e macica na porcao central de sua facies de nucleo. Os fenocristais, principalmente de quartzo, mas tambem feldspato potassico, mica e anfibolio, associados a zircao, criolita, polilitionita, pirocloro, cassiterita e minerais opacos, sao corroidos por uma matriz composta por albita, feldspato potassico, quartzo, cassiterita, criolita e minerais opacos, alem de fluorita secundaria. As variacoes mineralogicas e petrograficas observadas nos tres furos de sondagem estudados, localizados na porcao central do granito, sugerem que solucoes salinas ricas em agua exsolvidas a partir do mesmo corpo de magma permitiram a ocorrencia de reacoes de oxidacao e processos de criolitizacao, argilizacao e silicificacao que corroeram e substituiram os minerais magmaticos em um estagio tardio de sua historia de resfriamento. Palavras-chave: albita-granito, criolita, Pitinga, Granito Madeira, Proterozoico.

Mapeamento aerogamaespectrométrico da alteração hidrotermal associada à mineralização no distrito fluorítico de Santa Catarina, Brasil

The geophysical data processing (airborne gamma ray spectrometry) supplied the results in granites affected for the hidrotermal alteration in the Santa Catarina Fluorine District. The facies zonation in granites is associated to the granitic magmatism suggesting the rock fluor source. This lead to understanding the regional distribution of the fluorine deposits and defined new criteria for the prospecting of fluorine, space relations for the mineralization and the rock fluor source. This study shows that this source is situated in external portions of the Pedras Grandes Massif.