Esteve Cardellach

Strontium and sulphur isotope geochemistry of low-temperature barite-fluorite veins of the Catalonian Coastal Ranges (NE Spain): a fluid mixing model and age constraints

Sulphur and strontium isotope analyses from the low-temperature barite-fluorite veins of the Catalonian Coastal Ranges (NE Spain) reveal the nature and source of the ore-forming fluids and constrain the ages of the mineralizations. Sulphur isotope values in the barite δ34S = + 15 to + 20‰) are similar to those of sulphates in nearly Triassic-Jurassic evaporites δ34S = + 11 to + 19‰). 87Sr86Sr isotopic composition ratios of barites and fluorites are 0.7094–0.7167. The variation of 87Sr86Sr within individual veins suggests that the Sr had two different sources: granites rocks in the Hercynian basement and seawater or evaporites of Triassic-Early Jurassic age. Vein formation is modelled as a two-component mixing process in which the S and Sr isotopic composition of the end-members change with time. The observed difference in mean S and Sr isotopic compositions among the veins is interpreted to reflect differences in mineralization age. Ore deposition occurred between 225 and 195 Ma (Triassic to Early Jurassic) in all cases except the Berta mine which may be as young as Miocene.

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.

U–Pb dating of MVT ore-stage calcite: implications for fluid flow in a Mesozoic extensional basin from Iberian Peninsula

Abstract Fluid flow responsible for the formation of Mississippi Valley-type (MVT) deposits in the Cretaceous Maestrat Basin (Eastern Spain) has been constrained by means of U–Pb dating of cogenetic calcite and galena. A precise age ( 62.6±0.7 Ma ) has been obtained from an isochron that combines ore-stage calcite and galena from the Avecilla Mine. Unlike most MVT deposits, which are related to orogenic tectonic settings, the reported age indicates that Zn–Pb ores in the Maestrat Basin precipitated during rift or post-rift stages in Early Tertiary times. This study confirms that calcite–galena isochrons can be an effective tool to date MVT deposits.

Origin of vein hydrothermal carbonates in triassic limestones of / the Espadan Ranges Iberian Chain, E Spain

Dolomitization and Hg bearing veins in the lower Triassic limestones of the Espadan Ranges Iberian Chain, E of Spain ´ .

Fluid inclusions in pre-ore minerals from the carbonate-hosted mercury deposits in the Espadán Ranges (eastern Spain)

Abstract The fluids associated with pre-ore minerals in the carbonate-hosted mercury veins from the Espadan Ranges (eastern Spain) have been studied using microthermometry, Cryo-SEM-EDS, Raman spectroscopy and crush-leach analyses, in order to determine their origin and the processes responsible for mineralization. Three primary fluid inclusion types have been found in quartz and dolomite: (1) type S, composed of liquid + vapour (mainly CO 2 ) + halite; (2) type S-V, composed of liquid + high-density CO 2 double bubble + halite; and (3) type V, composed of high-density CO 2 N 2 mixtures. Type-S fluid inclusions are preferentially trapped in Betxi-type veins, characterized by the presence of hydrothermal dolomite, whereas type-V fluid inclusions are trapped almost exclusively in Eslida-type veins, which were without dolomite. From these data two different fluids can be inferred to occur during the period of formation of the veins: (1) a complex polysaline brine of NaClKClCaCl 2 (MgCl 2 , SO 4 2− )H 2 O composition with a salinity of up to 33 eq wt% NaCl; and a (2) CO 2 N 2 -rich fluid. The brine halogen composition points to its secondary origin caused by the dissolution of underlying marine evaporites. It is thought that these deposits were formed during Jurassic or Cretaceous rifting periods, as a consequence of fluid mixing between a high-salinity secondary brine and connate waters. The generation of a CO 2 N 2 -rich phase caused the pressure increase of the fluids that favoured the hydraulic fracturing of the enclosing rock (dolostone). The origin of this volatile-rich phase probably occurred due to the oxidation and thermochemical breakdown of the organic matter contained in the host rock. This event is recorded by the coetaneous trapping of both aqueous and carbonic fluids in quartz crystals. The formation conditions for the hypogene sulphide paragenesis are obscure but the coincidence between the preferential trapping of type-V fluid inclusions, the absence of hydrothermal dolomite and the major abundance of mercury in Eslida-type veins is thought to be linked to a mercury fractionation event to the vapour phase during the release of the volatiles.

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

Insights to controls on dolomitization by means of reactive transport models applied to the Benicàssim case study (Maestrat Basin, eastern Spain)

Partially dolomitized carbonate rocks of the Middle East and North America host large hydrocarbon reserves. The origin of some of these dolomites has been attributed to a hydrothermal mechanism. The Benicàssim area (Maestrat Basin, eastern Spain) constitutes an excellent field analogue for fault-controlled stratabound hydrothermal dolomitization: dolostone geobodies are well exposed and extend over several kilometres away from seismic-scale faults. This work investigates the main controls on the formation of stratabound versus massive dolomitization in carbonate sequences by means of two-dimensional (2D) reactive transport models applied to the Benicàssim case study. Simulation results suggest that the dolomitization capacity of Mg-rich fluids reaches a maximum at temperatures around 100 °C and a minimum at 25 °C (studied temperature range: 25–150 °C). It takes of the order of hundreds of thousands to millions of years to completely dolomitize kilometre-long limestone sections, with solutions flowing laterally through strata at velocities of metres per year (m/a). Permeability differences of two orders of magnitude between layers are required to form stratabound dolomitization. The kilometre-long stratabound dolostone geobodies of Benicàssim must have formed under a regime of lateral flux greater than metres per year over about a million years. As long-term dolomitization tends to produce massive dolostone bodies not seen at Benicàssim, the dolomitizing process there must have been limited by the availability of fluid volume or the flow-driving mechanism. Reactive transport simulations have proven a useful tool to quantify aspects of the Benicàssim genetic model of hydrothermal dolomitization.

Recurrent hydrothermal activity induced by successive extensional episodes: the case of the Berta F–(Pb–Zn) vein system (NE Spain)

Abstract A mineralogical and geochemical (fluid inclusion, stable and radiogenic isotopes) study of the Berta F–(Pb–Zn) vein system has identified the source and temperature of the fluid reservoirs involved and proved the existence of two separate hydrothermal events at the mine scale, which reflect distinct periods of regional fluid circulation. Main stage minerals (fluorite I, sulphides, calcite I and barite I) precipitated by mixing between a polysaline H 2 S bearing ( δ 34 S=11‰) brine (up to 23% NaCl eq salinity) and a more dilute fluid ( δ 18 O from −3.2‰ to 0‰), at temperatures between 80 and 150°C. The progressive increase in 87 Sr/ 86 Sr ratio from the early precipitated minerals (0.71242 in calcite I) to the late ones (0.71894 in fluorite II) is mainly (but not exclusively) due to a difference in age separating the two hydrothermal events. The assumed genetic model for the main stage fluorite (I) is based on a convective circulation of surficial waters leaching the crystalline basement rocks acquiring a high salinity, high 87 Sr/ 86 Sr ratios and a high temperature. These fluids then mixed with low salinity–low temperature waters, having a low 87 Sr/ 86 Sr ratio. An at least Jurassic age is suggested for the main period of vein filling, contemporaneous with the extensional regime during the Mesozoic, when fluid circulation was probably enhanced by crustal thinning. During the early Burdigalian (lower Miocene), a new period of important extension in this area took place. Hydrothermal activity related to this new and younger extensional regime is geochemically different and produced a distinctive mineralogical record, developing a set of veinlets filled with green octahedral fluorite (fluorite II), calcite (II) and barite (II). The Sr isotope compositions of these late stage vein minerals are compatible with leaching the granodiorite host-rocks during recent times. The existence of successive hydrothermal events in the same area is not surprising as geothermal systems, like La Garriga–Samalus, are still active and currently precipitating fluorite.

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.

Gold-bearing hedenbergite skarns from the SW contact of the Andorra granite (Central Pyrenees, Spain)

Several varieties of skarn outcrop have been found to develop along the contact between the Andorra granite and the Devonian limestones. The skarns contain variable amounts of gold ranging up to 5 g/t, always associated with sulphides. The sulphides in the skarn include arsenopyrite and pyrrhotite with lesser amounts of chalcopyrite, galena, sphalerite and Bi-minerals. Geothermometric and geobarometric data indicate the skarns formed at about 2 kbar and temperatures ranging from 500 ° to 350 °C from CO2-free polysaline brines at a slightly acidic pH and oxygen fugacity which decreases with time from the pyrite-pyrrhotite-magnetite towards the QFM buffer. Available data on gold solubility suggest that sufficient quantities of gold to form an ore deposit could have been transported as AuCl2-at the high temperatures and salinities under which the skarns formed. Both gold deposition and sulphide precipitation could have occurred due to a decrease in temperature and/or oxygen fugacity.