Silver-Bearing and Associated Minerals in El Zancudo Deposit, Antioquia, Colombia

The occurrence and the chemical compositions of ore minerals (especially the silver‐bearing minerals) and fluid inclusions of the El Zancudo mine in Colombia were investigated in order to analyze the genetic processes of the ore minerals and to examine the genesis of the deposit. The El Zancudo mine is a silver–gold deposit located in the western flank of the Central Cordillera in Antioquia Department. It consists mainly of banded ore veins hosted in greenschist and lesser disseminated ore in porphyritic rocks. The ore deposit is associated with extensive hydrothermally altered zones. The ores from the banded veins contain sphalerite, pyrite, arsenopyrite, galena, Ag‐bearing sulfosalts, Pb‐Sb sulfosalts, and minor chalcopyrite, electrum, and native silver. Electrum is included within sphalerite, pyrite, and arsenopyrite, and is also partially surrounded by pyrite, arsenopyrite, sphalerite, and tetrahedrite. Native silver is present in minor amounts as small grains in contact with Ag‐rich sulfosalts. Silver‐bearing sulfosalts are argentian tetrahedrite–freibergite solid solution, andorite, miargyrite, diaphorite, and owyheeite. Pb‐Sb sulfosalts are bournonite, jamesonite, and boulangerite. Two main crystallization stages are recognized, based on textural relations and mineral assemblages. The first‐stage assemblage includes sphalerite, pyrite, arsenopyrite, galena and electrum. The second stage is divided into two sub‐stages. The first sub‐stage commenced with the deposition and growth of sphalerite, pyrite, and arsenopyrite. These minerals are characterized by compositional growth banding, and seem to have crystallized continuously until the end of the second sub‐stage. Tetrahedrite, Pb‐Cu sulfosalts, Ag‐Sb sulfosalt, and Pb‐Ag‐Sb sulfosalts crystallized from the final part of the first sub‐stage and during the whole second sub‐stage. However, one Pb‐Ag‐Sb sulfosalt, diaphorite, was formed by a retrograde reaction between galena and miargyrite. The minimum and maximum genetic temperatures estimated from the FeS content of sphalerite coexisting with pyrite and the silver content of electrum are 300°C and 420°C, respectively. These estimated genetic temperatures are similar to, but slightly higher than the homogenization temperatures (235–350°C) of primary fluid inclusions in quartz. The presence of muscovite in the altered host rocks and gangue suggest that the pH of the hydrothermal solutions was close to neutral. Most of the sulfosalts in this deposit have previously been attributed as the products of epithermal mineralization. However, El Zancudo can be classified as a xenothermal deposit, in view of the low pressure and high temperature genetic conditions identified in the present study, based on the mineralogy of sulfosalts and the homogenization temperatures of the fluid inclusions.     

On the impact of atmospheric vs oceanic resolutions on the representation of the sea surface temperature in the South Eastern Tropical Atlantic

Climate Dynamics - Despite the efforts of the modelling community to improve the representation of the sea surface temperature (SST) over the South Eastern Tropical Atlantic, warm biases still...     

Photogrammetric techniques for monitoring tunnel deformation

This paper presents two innovative methods for tunnel monitoring that are based on digital photogrammetry. Both have been conceived to speed up operations that are currently accomplished by using engineering geodesy techniques and instruments. On the same time, proposed solutions are cheap and affordable. The first one is aimed at measuring relative deformations of transversal cross-section of tunnels. Some special targets are placed on the tunnel vault and their coordinates are measured by means of a small photogrammetric block made up of four images. A wire is used to setup the scale and to make all measurements comparable overtime. The second method can be applied for the measurement of vertical deformations along the longitudinal profile of tunnels. A new image-based approach called ‘photogrammetric levelling’ is discussed here, which is based on the metric rectification of each single image depicting a couple of special rods to be hung on levelling benchmarks. This technique can be used to replace traditional optical and digital level instruments. Both applications can be carried out by using a calibrated amateur camera. Some experiments in controlled and real environments allowed assessing performances and limitations of these techniques for operational surveys in tunnel monitoring.     

Exploring Changes in Biodiversity Through Pictures: A Citizen Science Experience

To accurately document the accelerated changes in biodiversity, scientists need an accurate historic baseline to which to compare the current state of a locale. These historic baselines are hard to come by, and specifically in the coastal principality of Asturias (northern Spain), biodiversity information before 1980 is scarce, fragmented, or entirely lacking. However, most families still keep old photographs, and we wondered if these historic documentations of the environment could provide missing baseline biodiversity data. We conducted a case study asking volunteers to find old family photographs, then return to the same place to retake the photograph from the same perspective. We compiled these photographs and analyzed the changes in biodiversity indices between the past and present. Thus, we quantified diversity changes in the region over the last century.     

Modelling of natural and synthetic polyelectrolyte interactions in natural waters by using SIT, Pitzer and Ion Pairing approaches

In this paper SIT and Pitzer models are used for the first time to describe the interactions of natural and synthetic polyelectrolytes in natural waters. Measurements were made potentiometrically at 25 °C in single electrolyte media, such as Et₄NI and NaCl (for fulvic acid 0.1 < I /mol L^− 1 < 0.75), and in a multi-component medium simulating the composition of natural waters at a wide range of salinities (for fulvic and alginic acids: 5 < S < 45) with particular reference to sea water [Synthetic Sea Water for Equilibrium studies, SSWE]. In order to simplify calculations, SSWE was considered to be a “single salt” BA, with cation B and anion A representing all the major cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) and anions (Cl⁻, SO₄²⁻) in natural sea water, respectively. The ion pair formation model was also applied to fulvate and alginate in artificial sea water by examining the interaction of polyanions with the single sea water cation. Results were compared with those obtained from previous speciation studies of synthetic polyelectrolytes (polyacrylic and polymethacrylic acids of different molecular weights). Results indicate that the SIT, Pitzer and Ion Pairing formation models used in studies of low molecular weight electrolytes may also be applied to polyelctrolytes with a few simple adjustments.     

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m³/day.

     

Structural study of synthetic mica–montmorillonite by means of 2D MAS NMR experiments

Syn-1, is a synthetic mica–montmorillonite interstratified mineral that forms one of the standard clay samples in the Clay Minerals Society Source Clays Project. However, there are still controversies regarding some structural aspects such as the interlayer composition or the location of the extra-aluminium determined by chemical analysis. The main objective of this paper is to shed light on those structural aspects that affect the reactivity of the interstratified minerals. For this purpose, we have used ¹ H–²⁹ Si and ¹ H–²⁷Al HETCOR MAS NMR to show that it is likely that the interlayer space of the beidellite part is composed of ammonium ions whereas ammonium and aluminium ions are responsible for the charge balance in the mica type layer.     

Comparative toxic effects of copper-based nanoparticles and their microparticles in Daphnia magna by using natural freshwater media

Copper-based nanoparticles (NPs) are being widely used in different application fields and their health impacts to aquatic environments represent a current concern. Few studies are available about their comparative toxicity with their bulks and ions under natural exposition in aquatic organisms. Thus, the toxicity of Cu and CuO NPs and their microparticle and ionic forms was assayed in the acute immobilisation test of Daphnia magna by using freshwater media. Electronic microscopy, laser doppler velocimetry, and dynamic laser scattering methodologies were used to NPs characterisation. The results indicated that CuNPs and CuONPs were more toxic than their microparticles. Among NPs, CuNPs showed higher toxicity than CuONPs. Copper-based nanoparticles showed similar hydrodynamic particle size and were agglomerated in culture media, suggesting toxic-ionic release relationship and corroborated by the high toxicity induced by CuSO₄. Additionally, water chemistry of natural freshwater used in the experiments also favoured the ion release of these NPs.