Bismuth‐melt trails trapped in cassiterite–quartz veins

Native bismuth in the form of metallic melt has been considered instrumental to the formation of some metallic ore deposits via a mechanism dubbed the “Liquid Bismuth Collector Model.” Here, we provide petrographical documentation of trail‐forming, μm‐sized blebs of native bismuth in cassiterite–quartz veins from the Santa Bárbara greisen Sn deposit in the Rondônia tin province of northern Brazil. These inclusions suggest the trapping of a Bi melt that took place during vein formation, in a mechanism similar to the entrapment of fluid inclusions.     

Soil contamination by metals with high ecological risk in urban and rural areas

Industrial development, intensive agriculture and fast urbanization have caused the metal contents of soils to increase to many times the allowable limits. To assess this impact on urban and rural soils, we quantified the Cd, Cr, Cu, Pb, Ni and Zn contents of 258 soil samples from the Recife metropolitan region (RMR). The objectives of the study were to estimate the probability of ecological risk, to determine the spatial pattern of the metals’ accumulation in the soil and to identify potential sources for the metals using a multivariate geostatistical approach. Mean concentrations of Zn, Cr, Pb, Cu, Ni and Cd in soils were 65.2, 17.9, 16.5, 12.8, 6.3 and 1.5 mg kg^?1, respectively. The results demonstrated that the Cd was anthropogenic in origin, the Cr and Ni were lithogenic (natural) in origin and the Cu, Pb and Zn were mixed in origin. Cd contaminated 91% of the samples; the median content of Cd (1.4 mg kg^?1) was three times the quality reference value for soil. The Cd contents of sugarcane fields exceeded the allowable limit (3.0 mg kg^?1) for agricultural areas. The spatial variability of the metals in the RMR showed that metallurgy, cement production, vehicle exhaust and vehicular traffic were the main sources of metals in urban areas, while phosphate-based fertilizers were the main sources in rural areas. More than 80% of the metropolitan region surveyed in the study was at moderate to high ecological risk.     

Tracing source and evolution of suspended particles in the Rio Negro Basin (Brazil) using chemical species of iron

Suspended solids found in porewaters obtained in waterlogged soil sequences that included representative laterite–podzol transitions, associated brooks and major rivers of the Rio Negro watershed (Brazil) were studied using electron paramagnetic resonance (EPR) and Fourier-transform infrared spectroscopies. The main goal was to ascertain sources and track the evolution of suspended matter using a ubiquitous chemical species, FeIII complexed to organic matter (FeOM). Three size fractions were separated by tangential-flow (ultra)filtration: particulate (> 0.2 μm), dense (P) and light (Ps), and colloidal (5 kD < Col. < 0.2 μm) fractions. Quantitative results were acquired for Col. and Ps fractions which are predominantly organic in nature.FeOM concentration (in ‰ dry weight) was determined to be relatively low in suspended solids found in black waters from podzol porewaters and brooks whereas in the main rivers it was several times higher. FeOM concentrations were also correlated with Fe(II)/Fe(III) ratios in solution; these ratios were high in podzol porewaters and low in the rivers. Considering that organic complexation of Fe(II) is minor when compared to that of Fe(III), two interpretations were proposed to account for the above observation. First, [FeOM] was assumed to be distributed along a mixing line, with the clear waters from laterites and the black waters from podzols being its end-members. Consequently, [FeOM] can be used to trace the source of suspended material. Second, dissolved Fe(II) from podzol areas was considered to be progressively oxidized as pore waters move towards the mainstream. According to this mechanism, iron is complexed by organic matter or precipitated as oxides, thus producing an evolution of colloidal matter. As a result of these mechanisms' action, both the high production of Fe(II) and organic matter at the waterlogged podzol–laterite transition areas are major factors affecting iron export in the Rio Negro watershed.     

Groundwater behaviour in Madeira, volcanic island (Portugal)

Madeira Island is a hot-spot originating from a mantle plume. K-Ar age determinations indicate that the emerged part of the island was generated during Post-Miocene times 6000–7000 years B.P. Groundwater occurs in perched-water bodies, spring discharge from them is high, about 3,650 l/s; in dike-impounded water and basal groundwater. Basal groundwater is exploited by tunnels (1,100 l/s) and wells (1,100 l/s). Hydraulic gradients range from 10^–4 to 10^–2 and transmissivity ranges from 1.16×10^–2 to 2.89×10^–1 m²/s, indicating the heterogeneity of the volcanic aquifers. Water mineralisation is variable, and electrical conductivity ranges from 50 to 3,300 S/cm. There is a difference between groundwater discharging from perched-water bodies (43–201 S/cm) and from basal groundwater (109–3,300 S/cm). Groundwater average pH is 7.37, with waters acid to slightly alkaline (6.13–8.4), and generally cold. Nevertheless, a few samples associated with fault zones can be classified as thermal waters.

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Resumen La Isla de Madeira tuvo origen en un punto caliente proveniente de una pluma del manto. Las dataciones K – Ar, indican que la parte emergida de la isla se formó durante en Post—Mioceno, hace unos 6000–7000 años. El agua subterránea se encuentra en acuíferos colgados, cuya descarga a través de manantiales es alta, alrededor de 3650 l/s; también como agua retenida en diques o bien como agua subterránea propiamente dicha. Esta última es explotada por túneles (1100 l/s) y pozos (1100 l/s). Los gradientes hidráulicos varían desde 10–4 hasta 10–2 y la transmisividad varía desde 1.16×10^–2 hasta 2.89×10^–1 m²/s, indicando la heterogeneidad de los acuíferos volcánicos. La mineralización de agua es variable y la conductividad eléctrica varía desde 50 mS/cm hasta 3300 mS/cm. Hay una diferencia entre el agua subterránea proveniente de acuíferos colgados (43–201 mS/cm) y aquella del acuífero principal (109–3300 mS/cm). El pH promedio para el agua subterránea es 7.37; con variación desde ácida hasta ligeramente alcalina (6.13–8.4), y es generalmente fría. Sin embargo unos pocos ejemplos asociados con zonas de falla, pueden ser clasificados como agua termal.

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Résumé Lîle de Madeira est un point chaud, provenant dun panache mantélique. Les datations par la méthode de K-Ar indiquent que la part émergée de lîle a été générée pendant le Post Miocène, il y a 6000–7000 ans. Les eaux souterraines sont cantonnées dans des aquifères perchées qui se déchargent par des sources à grands débits, avec des valeurs dapproximativement de 3500 l/s, ainsi que dans les dikes. Une importante quantité des eaux souterraine se trouve sur la forme deau de fonds, formant une nappe basale, qui est exploitée par des tunnels (1100 l/s) et par des puits (1100 l/s). Les gradients hydrauliques ont des valeurs dans lintervalle de 10^–2 à 10^–4, tandis que les transmissivités se rangent entre 1.16×10^–2 m²/s et 2.81×10^–1 m²/s, ce quindique la hétérogénéité de laquifère volcanique. La minéralisation des eaux est aussi variable avec des conductivités électriques qui se rangent ente 50 mS/cm et 3300 mS/cm. Il y a une différence entre la conductivité des eaux provenant des aquifères perchées (30–201 mS/cm) par rapport à la conductivité les eaux de la nappe basale (109–3300 mS/cm). Le pH moyen est de 7.37 avec des valeurs de 6.13 pour les eaux acides et de 8.4 pour les eaux à faible alcalinité. En général il sagit des eaux froides, mais quelques échantillons provenant des zones faillées peuvent être classifiés comme des eaux thermales.

     

Wave observations from an array of directional buoys over the southern Brazilian coast

It is well known that the majority of buoy measurements are located around the US coast and along some Europeans countries. The lack of long-term and densely spaced in situ measurements in the Southern Hemisphere in general, and the South Atlantic in particular, hinders several investigations due to the lack of detailed metocean information. Here, we present an effort to overcome this limitation, with a dense network of buoys along the Brazilian coast, equipped with several meteorological and oceanographic sensors. Out of ten currently operational buoys, three are employed to present the main characteristics of waves in the Southern part of the network. For the first time, sensor characteristics and settings are described, as well as the methods applied to the raw wave data. Statistics and distributions of wave parameters, swell propagating events, comparison with a numerical model and altimeters and a discussion about the occurrence of freak waves are presented.     

Settlement Analysis of Açu Dam,Brazil

Geotechnical and Geological Engineering - The Armando Ribeiro Gonçalves Dam, popularly known as The Açu Dam, is an important geotechnical construction in Rio Grande do Norte state,...     

Induced seismicity in the Castanhão reservoir, NE Brazil — Preliminary results

The Castanhão reservoir was built in the state of Ceará, a dry region in Northeastern Brazil, to regulate the flow of the Jaguaribe River, for irrigation, and for power generation. It is an earth-filled dam, 60 m high, with a water capacity of 4.5 × 10⁹ m³. The seismicity in the area has been monitored since 1998, with a few interruptions, using one analog or one digital station and, during a few periods, a three-station network. The first earthquakes likely to be induced events were detected in 2003, when the water level was about 20 m high. In early 2004 a very heavy rainfall season quickly filled the reservoir. Shortly after, an increase in the seismic activity occurred and many micro-earthquakes were recorded. We suggest that this activity resulted from an increase in pore pressure due to undrained response. Therefore, we may classify this cluster of micro-earthquakes as “initial seismicity.” We deployed a network with four analog stations in the area, following this activity, to determine the epicentral zone. At least three epicentral areas under the reservoir were detected. The spatio-temporal analysis of the available data revealed that the seismicity occurs in clusters and that these were activated at different periods. We identified four sets of faults (N–S-, E–W-, NW–SE-, and NE–SW-oriented), some of which moved in shallow crustal levels and as recently as the Quaternary (1.8 Ma). Under the present-day stress regime, the last two sets moved as strike-slip structures. We suggest a possible correlation between dormant faults and the observed induced seismicity.     

Lead isotope distribution and enrichment factors in soil profiles around an abandoned Pb-smelter plant

Todos os Santos (all Saints) Bay area on Brazil’s east coast is known for one of the most significant cases of lead contamination in the country owing to the past activities of a Pb-smelter plant. This work was carried out to assess the concentration and sources of Pb based on Pb isotopes and enrichment factor of soil profiles surrounding Todos os Santos Bay in order to understand the expansion of contamination and to help the establishment of Pb regulatory standards for the region. Forty-four samples were collected from soil genetic horizons of six pedons that represent the range of dominant soil properties and geologic materials in the region. Concentrations of Pb and the isotopes ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb were determined on an inductively coupled plasma (quadrupole) mass spectrometry. The soil enrichment factor was calculated using Al and Fe as conservative index elements. Average Pb concentration (15.87 mg kg^?1) in uppermost horizons (from all six pedons) is slightly higher than soil background concentrations commonly reported in Brazil. Samples feature a wide range of Pb isotope ratios, ranging from 36.71 to 47.38 for ²⁰⁸Pb/²⁰⁴Pb, 15.00 to 15.65 for ²⁰⁷Pb/²⁰⁴Pb, 16.86 to 20.59 for ²⁰⁶Pb/²⁰⁴Pb, and 1.10 to 1.31 for ²⁰⁶Pb/²⁰⁷Pb. For the enrichment factor calculations, only Fe demonstrated a good agreement with Pb isotopic ratios. Both Pb isotopic composition and enrichment factor were useful tools to distinguishing natural and anthropogenic influence on the Pb soil concentrations.