Procedia Earth and Planetary Science最新文献

On the smooth seafloor of exhumed mantle-rocks of the slow-spreading Southwest Indian Ridge, the secondary oxide and carbonate mineralizations record specific chemical signatures of the alteration of serpentinites by low-temperature hydrothermal seawater-dominated fluids. The uncommon characteristics of Fe-oxides forming nodule cortex or thick encrustments are their high Si, low Mn contents, trace elements (e.g. Cr) and REE behavior. Oxides composition evolves through time. Associated to oxides, carbonates (aragonite, calcite, dolomite) characterize the matrix of young indurated serpentinite breccias found at ridge axis. Such mineralogical and geochemical sequences trace, as proxies, the ongoing mantle-exhumation and serpentinization process linked to the detachment faults, and the late alteration reactions that impact on crust–ocean transfers and oceanic budget.

Hydrochemical and isotopic characterization of mine water having connections with groundwater and surface water at Zlatna gold mining area (Apuseni Mountains, Romania) was performed to provide insights on mine site emissions with the surrounding environment after the cessation of mining operations. The mine water coming into direct contact with mineralization is more acidic than the mine water that only interacts with the host rock. Light isotopic composition of most mine water suggests snowmelt and high altitude precipitations as the main source of recharge. Linear correlation between δD and δ¹⁸O values indicates that all water sources belong to the meteoric cycle. For most mine water sources no significant seasonal variations of the δD, δ¹⁸O, pH and TDS values was recorded, indicating well-mixed underground systems and slow flow recharge pathways. Other mine water sources show seasonal variations of these parameters suggesting continuous recharge of mine water and a fast underground circulation. No relevant contamination of springs and phreatic water by mine water could be revealed, suggesting different underground pathways for the two types of water. On the contrary, running water is contaminated by mine water and the negative effects of acid mine drainage occur mainly in the summer months when the debit of the running water decreases.

We present the results of an experimental study of the effect of anisotropy on the kinetics of K-Feldspar dissolution under hydrothermal conditions as encountered in the Soultz-sous-Forêts enhanced geothermal system. We try to quantify the impact of K-feldspar anisotropy on dissolution rates in order to develop a more comprehensive model of the evolution of the reactive surface of silicate minerals in order to propose alternate kinetic rate laws to be implemented into water-rock interaction models and reactive transport codes. Our results evidence a relation between K-spar dissolution rate and the Gibbs free energy of reaction (ΔG_r) which clearly differs from the transition state theory usually implemented into geochemical codes: it depends on the crystallographic orientation of K-spar mineral with significant differences between the different crystal faces. As for the far-from-equilibrium dissolution rate, this result highlights that using a unique theoretical rate law to describe dissolution rate as a function of ΔG_r remains highly questionable. These results are very important for our challenge of understanding and modelling the dissolution mechanisms and they evidence that the dissolution anisotropy plays a fundamental role in these mechanisms.

Many alpine valleys have inherited strong industrial remnants. Chemical and metallurgical companies were set up in these narrow glacial valleys at the beginning of the industrial era to benefit from cheap labor and hydroelectricity. Regulations concerning solid and liquid waste handling did not exist, and contaminated sediments were often used as soil amendment to improve soil texture, spreading the contamination, which local Authorities have now to deal with.

In the present study we report on mercury contamination in the narrow alpine valley known as canton of Valais valley. Waste materials and contaminated sediments were deposited in the valley for many years. An electromagnetic conductivity survey allowed a definitive mapping of the extent of such practices because an EM conductivity contrast was clearly detectable between the added silty-clay material and the natural silty-sand soil. High EM conductivity correlates quite well with high Hg surface soil content. Cores drilled at hotspots and along the canal were analyzed for total mercury, methyl mercury, and core sedimentary features recorded. While up to 70 cm thick, dredged, Hg-contaminated material was found to lay above the original sandy soil in housing areas, the mercury contamination extends down to 1.5 m depth, i.e. down to the water table, probably caused by the high sediment material organic content (OC), and OC-Hg enhanced transport. Methylation reductive conditions were observed, together with high MeHg relative abundance ([MeHg]/ [HgT] > 0.1%), in two environments, namely the zone of fluctuating water table and the canal water/sediment interface. Groundwater quality was not impacted, because of large groundwater fluxes observed in these glacial alpine valleys.