Mercè Corbella

Immobilization of Cu, Pb and Zn in mine-contaminated soils using reactive materials

Immobilization processes were used to chemically stabilize soil contaminated with Cu, Pb and Zn from mine tailings and industrial impoundments. We examined the effectiveness of ordinary Portland cement (OPC), phosphoric acid and MgO at immobilizing Cu, Pb and Zn in soil contaminated by either mine tailings or industrial and mine wastes. The effectiveness was evaluated using column leaching experiments and geochemical modelling, in which we assessed possible mechanisms for metal immobilization using PHREEQC and Medusa numerical codes. Experimental results showed that Cu was mobilized in all the experiments, whereas Pb immobilization with H(3)PO(4) may have been related to the precipitation of chloropyromorphite. Thus, the Pb concentrations of leachates of pure mining and industrial contaminated soils (32-410 μg/l and 430-1000 μg/l, respectively) were reduced to 1-60 and 3-360 μg/l, respectively, in the phosphoric acid experiment. The mobilization of Pb at high alkaline conditions, when Pb(OH)(4)(-) is the most stable species, may be the main obstacle to the use of OPC and MgO in the immobilization of this metal. In the mining- and industry-contaminated soil, Zn was retained by OPC but removed by MgO. The experiments with OPC showed the Zn decrease in the leachates of mining soil from 226-1960 μg/l to 92-121 μg/l. In the industrial contaminated soil, the Zn decrease in the leachates was most elevated, showing >2500 μg/l in the leachates of contaminated soil and 76-173 μg/l in the OPC experiment. Finally, when H(3)PO(4) was added, Zn was mobilized.

Geology of the Cerro Quema Au-Cu deposit (Azuero Peninsula, Panama)

The Cerro Quema district, located on the Azuero Peninsula, Panama, is part of a large regional hydrothermal system controlled by regional faults striking broadly E-W, developed within the Rio Quema Formation. This formation is composed of volcanic, sedimentary and volcano-sedimentary rocks indicating a submarine depositional environment, corresponding to the fore-arc basin of a Cretaceous–Paleogene volcanic arc. The structures observed in the area and their tectono-stratigraphic relationship with the surrounding formations suggest a compressive and/or transpressive tectonic regime, at least during Late Cretaceous–Oligocene times. The igneous rocks of the Rio Quema Formation plot within the calc-alkaline field with trace and rare earth element (REE) patterns of volcanic arc affinity. This volcanic arc developed on the Caribbean large igneous province during subduction of the Farallon Plate. Mineralization consists of disseminations of pyrite and enargite as well as a stockwork of pyrite and barite with minor sphalerite, galena and chalcopyrite, hosted by a subaqueous dacitic lava dome of the Rio Quema Formation. Gold is present as submicroscopic grains and associated with pyrite as invisible gold. A hydrothermal alteration pattern with a core of advanced argillic alteration (vuggy silica with alunite, dickite, pyrite and enargite) and an outer zone of argillic alteration (kaolinite, smectite and illite) has been observed. Supergene oxidation overprinted the hydrothermal alteration resulting in a thick cap of residual silica and iron oxides. The ore minerals, the alteration pattern and the tectono-volcanic environment of Cerro Quema are consistent with a high sulfidation epithermal system developed in the Azuero peninsula during pre-Oligocene times

Dissolution of deep carbonate rocks by fluid mixing: a discussion based on reactive transport modeling

Abstract The geochemical processes proposed until now to explain the formation of cavities in deep carbonates are difficult to reconcile with observations. We propose a mixing model of hydrothermal solutions equilibrated with carbonate. Through numerical reactive transport simulations, we observe that chemical mixing of hydrothermal solutions can generate a zone of host rock dissolution and another of minor calcite precipitation. Variations in relative fluid velocities, pH or S content may result in the growth of the precipitation zone with respect to the dissolution one. This explains the finding of dissolution cavities in carbonate rocks with subsequent filling by carbonate minerals.

Reactivity of Dolomitizing Fluids and Evaluation of Mg Sources in the Benicassim Area (Maestrat Basin, E Spain)

Hydrothermal dolomitization is one of the most important processes in enhancing or degrading carbonate porosity and permeability. This type of dolomite forms due to the circulation and/or mixing of different types of solutions, mainly seawater-derived or deep brines. The Lower Cretaceous Benicassim dolomitized ramp is an excellent example to study and evaluate the impact of hydrothermal dolomitization on reservoir quality distribution. In this contribution, the possible magnesium sources for the Benicassim case study are evaluated, as well as the reactivity of different dolomitizing fluids at variable temperatures. The results show that dolomitization at Benicassim occurred due to the circulation of a high temperature (> 80oC) fluid that had its origin from evolved seawater that interacted with K-rich rocks, probably from the Paleozoic basement. Reactivity evaluation of four possible dolomitizing fluids, by means of geochemical modelling, reveals that evolved seawater can be considerably more reactive than high-salinity brines. Fluid mixing between seawater and saline brines at 100 oC does not seem to affect the volume of fluid required to dolomitize the whole rock, but it considerably alters the saturation index of calcite. The variation of saturation index is a strongly non-linear process when two fluids are mixed.

Flow Patterns of Dolomitizing Solutions in a Buried Carbonate Ramp – The Benicassim Case Study (Maestrat Basin, NE Spain)

Geometric, petrographic, and geochemical observations suggest that sub-stratiform dolomitization in a Lower Cretaceous Benicassim ramp (Maestrat Basin, E Spain) was due to the circulation of high temperature brines through faults and high permeability layers. In this study, fluid and heat flow numerical simulations are applied to investigate the controls on hydrothermal flow in this area, depending on the tectonic activity at the time of dolomitization. The results indicate that flow caused by rapid release of overpressured fluids below seals in recurrent pulses through large-scale faults may drive enough fluid for dolomitization, but not enough heat. Thermal conduction dominates advection over large-time scale. However, long-term fluid circulation, due to differences in pressure and temperature within the basin, can pump dolomitizing fluids at high temperature during long periods of time if the system is open. Moreover, a permeability contrast of two orders of magnitude is required to have lateral flow preferentially in some layers and to form relatively sharp, sub-stratiform dolomitization fronts.

Laser scanning confocal microscopy characterization of water repellent distribution in a sandstone pore network

In the present work, we propose the use of the Laser Scanning Confocal Microscopy (LSCM) to determine the effect of water repellents on rocks pore‐network configuration and interconnection. The rocks studied are sandstones of Miocene age, a building material that is commonly found in the architectural heritage of Tunisia. The porosity quantitative data of treated and untreated samples, obtained by mercury porosimetry tests, were compared. The results show a slight decrease in total porosity with the water repellent treatment, which reduced both microporosity and macroporosity. This reduction produced a modification in pore size distribution and a shift of the pore access size mode interval toward smaller pore diameters (from the 30–40 μm to the 20–30 μm intervals). The water repellent was observed in SEM images as a continuous film coating grain surfaces; moreover, it was easily visualized in LSCM, by staining the water repellent with Epodye fluorochrome, and the coating thickness was straightforwardly measured (1.5–2 μm). In fact, the combination of mercury intrusion porosimetry data and LSCM observations suggests that the porosity reduction and the shift of the pore diameter mode were mainly due to the general reduction of pore diameters, but also to the plugging of the smallest pores (less than 3–4 μm in diameter) by the water repellent film. Finally, the LSCM technique enabled the reconstruction of 3D views of the water repellent coating film in the pore network, indicating that its distribution was uniform and continuous over the 100 μm thick sample. The LSCM imaging facilitates the integration and interpretation of mercury porosimetry and SEM data. Microsc. Res. Tech., 2008.

Relationship between Dolomite Textures and Formation Temperature - Insights from the Riópar Area (Betic basin, SE Spain)

This study reports textures and homogenization temperatures of primary fluid inclusions on dolomites hosted in Upper Jurassic to Lower Cretaceous age carbonate sequence from the Riopar area (Mesozoic Prebetic Basin, SE Spain). Five dolomite texture-types have been identified: i) planar subhedral replacive dolomite (ReD); ii) transition between planar subhedral to euhedral dolomite (ReD-SuD); iii) planar euhedral sucrosic dolomite (SuD); iv) non-planar cloudy saddle dolomite (SaD-I); and v) non-planar clear saddle dolomite (SaD-II). Fluid inclusions in ReD-SuD dolomite show a Th mode value of 205oC, while SaD-I and SaD-II show Th mode values of 235oC and 195oC respectively. Our research indicates that planar and non-planar dolomite textures are formed at high-temperatures under hydrothermal conditions in deep-burial diagenetic environments, unsupporting the accepted idea that planar dolomites are formed under temperatures around or less than 50-60oC in shallow-burial diagenetic environments.