Heavy metal contamination in the Arieş river catchment, western Romania: Implications for development of the Roşia Montană gold deposit

The Abrud–Arieş river system, western Romania, is subject to ongoing mining activity associated with Cu, Pb and Zn ore extraction. The catchment contains what is believed to be Europe's largest unutilized Au deposit at Roşia Montană that is planned to be exploited by open-cast mining techniques. The magnitude and environmental significance of metal (Cd, Cu, Pb, and Zn) concentrations in surface water and river channel sediment have been investigated along a 140 km reach of the Rivers Abrud and Arieş and 9 tributaries affected by mining. The speciation of sediment-bound metals was established using a 4-stage sequential extraction procedure (SEP) that identified four chemical phases: (1) exchangeable, (2) Fe/Mn oxides, (3) organic matter/sulphides and (4) residual. Peak solute and sediment-bound metal concentrations were found to occur in the River Abrud downstream of the EM Bucium mine and in mining-affected tributaries, with up to 71% of sites containing sediment metal concentrations in excess of Dutch intervention values. The River Arieş was found to be much less polluted than the River Abrud, with only Cu showing concentrations above guideline values, as a consequence of porphyry Cu mineralization in the catchment. The magnitude and spatial extent of metal pollution is influenced by local physico-chemical conditions and hydrological linkages between mining and local river systems. Sediment-bound Cd and Zn were found to be predominantly associated with the exchangeable phase of the sediment (9–74% and 6–65%, respectively), whilst Fe/Mn oxides (5–76%) and organic matter/sulphides (1–45%) generally accounted for a majority of Pb and Cu partitioning, respectively. Sites of environmentally significant sediment-metal pollution were identified in the Rivers Abrud and Arieş where exchangeable metal concentrations exceeded Dutch intervention values. The implications of metal contamination in the Arieş river basin to the proposed mining development at Roşia Montana are discussed in relation to other contaminated Romanian catchments and with the EU Water Framework Directive.     

The Morphological and Optical Properties of Volcanic Glass: A Tool to Assess Density-induced Vertical Migration of Tephra in Sediment Cores

Volcanic ash layers in sediment cores are valuable geochronological markers in paleolimnological research. The composition of volcanic glass is related to identifiable, chronologically distinctive volcanic eruptions. Consequently, tephra layers provide time horizons allowing regional-scale correlations for lake sediments. Volcanic glass is often present in samples routinely prepared by paleolimnologists such as diatom slides and thin sections. Knowledge of the morphological and optical properties of volcanic glass allows for its identification. This is essential for the identification of ash layers that are not macroscopically visible or to track their vertical migration in soft organic sediments. The purposes of this note are to: (1) describe how the morphological (i.e., shape, vesicularity) and optical (i.e., refractive index and birefringence) properties can be used to identify volcanic glass in preparations from lake sediments; and (2) show how the quantification of volcanic glass from diatom slides is used to quantify the density-induced displacement of a 4.5 cm-thick Mazama ash-layer through organic sediments and to approximate its timing of initial deposition.     

Structural controls on groundwater flow in a fractured bedrock aquifer underlying an agricultural region of northwestern New Brunswick,Canada

A hydrogeological study was conducted in northwestern New Brunswick, Canada, to improve the predictability of fracture-dominated groundwater flow within folded bedrock composed of fine-grained turbidites. Borehole televiewer logging and outcrop mapping, integrated with hydraulic packer tests revealed enhanced hydraulic conductivity associated with northeasterly striking bedding-plane fractures formed during folding and flexural slip. These fractures impart azimuthal anisotropy to the aquifer because of moderately dipping fold limbs. High-angle fractures form a well-developed non-stratabound network, comprising two open fracture sets striking NNE parallel to the current direction of principal stress, and WNW parallel to the direction of principal stress that dominated during the Acadian orogeny. The subset of fractures showing significant oxidation, deemed most important to the groundwater flow system, is dominated by bedding-plane and high-angle fractures striking near-parallel to the maximum principal stress direction, resulting in extensional opening and enhanced hydraulic conductivities. An equivalent porous media model, incorporating anisotropy and varying hydraulic conductivity with depth, indicates that horizontal flow dominates the aquifer with relatively minor exchange between different model layers. These findings have implications for understanding flow directions in the Black Brook Watershed and elsewhere in the Matapédia Basin where fractures formed under similar stress conditions.