Marguerite Munoz

Multi-stage fluid incursion in the Palaeozoic basement-hosted Saint-Salvy ore deposit (NW Montagne Noire, southern France)

Abstract The Saint-Salvy vein-hosted Zn (+Ge) deposit occurs in an E–W fault system which flanks the southern margin of the late Variscan Sidobre granite, and cross-cuts Cambrian black shales of the Palaeozoic basement. Comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events (M1–M4) related to late and post-Variscan tectonic events. A further late-stage event may be related to weathering. M1 (=skarn deposits) and M2 (=patchily mineralized quartz veinlets) are associated with granite emplacement. Quartz contains low salinity, H2O CO2 (NaCl)-dominated fluids(⩽6wt% NaCl equiv.) of relatively high temperature (300–580°C), trapped under moderate to high pressure. Estimated M1 fluid δD and calculated fluidδ18O plot within the metamorphic water field. There appears to be no involvement of magmatic fluids. By contrast, M3 (= barren quartz) and M4 (= zinciferous economic mineralization) stages have H2O CO2 NaCl CaCl2 fluid inclusions with high salinities (23–25 wt% NaCl equiv.) and low temperatures(∼ 80–140°C), which were trapped under low-pressure conditions. The high salinity and NaCl + CaCl2 content of both M3 and M4 indicates that their parent fluids leached evaporitic salts. M3 fluids are meteoric water dominated, falling close to the meteoric water line (δD andδ18O averaging −64 and −8‰, respectively). M4 fluids have highly distinctive δD averaging −101‰, and calculated fluidδ18O varying from−1.2to+7.1‰. The unusually low δD composition of M4 suggests the involvement of “organic” fluids, in which H is derived directly or indirectly from organic matter. The relatively highδ18O of M4 fluids indicates that considerable isotopic exchange with sedimentary material took place, displacing theδ18O from the meteoric water line. The data imply interaction of meteoric waters with evaporite and hydrocarbon-bearing sedimentary sequences, most probably the adjacent Aquitain Basin. The main economic mineralization (M4 stage) took place during a tensional event, probably coincident with the Lias-Dogger transition. Calculatedδ34SH2S of M4 sulphide(+5.4to+8.2‰) is almost identical toδ34S of local Cambrian sulphides(+4.7to+9.4‰) suggesting a genetic link. Abundant siderite associated with M4 sphalerite hasδ13C ranging from−2.6to−4.4‰ indicating that carbon was sourced from sedimentary carbonate mobilized by, or equilibrated with the hydrothermal fluid. Late-stage sulphides exhibit extraordinary and highly distinctiveδ34S. Sphalerite has extremely low δ34S(−42.5to−50.5‰), whereas pyrite has an extraordinary large range from−33.2‰to+74.3‰. Closed system sulphate reduction is held to be responsible for the extremely highδ34S: whereas more open system reduction produces the very low values. The coincidence of isotopically lowδ13C(−7.6to−11.9‰) for co-genetic calcite suggests the involvement of organic matter in the reduction process.

Health risk assessment for human exposure by direct ingestion of Pb, Cd, Zn bearing dust in the former miners’ village of Jebel Ressas (NE Tunisia)

Mining activity in Jebel Ressas (1880–1956) generated important quantities of wastes. The former miners’ village is expanding very close to the waste dumps which are highly concentrated in Pb, Zn and Cd. Under the semi-arid Mediterranean climate, wind erosion triggers the transport of contaminated dust towards the village. A health risk may exist for inhabitants related to their exposure to contaminated dust via ingestion, inhalation and dermal contact. This study is dedicated to the evaluation of the health risk after direct ingestion of dusts. Seven samples of dusts were collected in living places over the village. Anomalous metal concentrations in dusts range respectively from 0.16 wt% to 1.14 wt% of Pb, 0.35 wt% to 2.49 wt% of Zn and 14 to 109 mg/kg of Cd. SEM-EDS analysis of the dust particles shows that calcite is dominant and that metalliferous minerals are mainly Pb and Zn carbonates and Zn silicates. Iron oxy-hydroxides exist in small proportions and Pb and Zn sulfides are scarce. Modeling the quantity of dissolved metals in a simulated gastric fluid was performed taking into account the dust mineralogy and the daily ingested quantities of dust, ranging from 100 mg for adults to 200 mg for children. The ratio of dissolved metals to initially ingested ones defines the bioaccessibility factor. It gives the fraction of metals able to reach the blood through the intestinal wall. Modeling the dissolution of two dust samples, the most and the less concentrated ones in metals, was performed considering a gastric fluid with two extreme pH values (0.93 and 5.0). All dust minerals totally dissolve except cerussite for the most concentrated sample in a gastric fluid of pH 5. Therefore, the bioaccessibility factor of Zn and Cd is equal to 1, that of Pb ranges between 0.27 and 1. Then, an estimation of the occurrence of risk was calculated from the ratio of the daily exposure dose by direct ingestion and the reference dose. The risk occurs with a ratio above 1. The global risk of ingestion of three metals is high for the children, especially for Pb with a ratio reaching 39. The risk for adults appears for Pb with a ratio of 4.6 in the case of ingestion of most concentrated dusts. However, the integration of the other routes of exposure in the calculation of the risk must be taken into account for a thorough estimation.

Continental basinal origin of ore fluids from southwestern Massif central fluorite veins (Albigeois, France): evidence from fluid inclusion and stable isotope analyses

The most important fluorspar mining district in France is located in the Palaeozoic basement of the Albigeois in southwestern French Massif Central. The massive fluorite is hosted within large E–W striking fractures, crosscutting Cambro–Ordovician clastics, associated with large zones of hypersilicified tectonic breccia which form the wall of the mined deposits. Fluid inclusion data for pre-fluorite and fluorite stage fluids have salinities between 20–26 wt% NaCl equiv., with homogenisation temperatures between 85–170°C. Furthermore, low first ice melting temperatures (around −50°C) indicates the presence of significant CaCl2 and possibly MgCl2 together with NaCl. Calculated fluid δ18O for pre-fluorite quartz ranges from −9.1‰ to −5.2‰, with δD between −55‰ to −64‰, placing the data directly on the present day meteoric water line. Fluorite stage fluids have δ18O between +0.1‰ to +3.2‰, and δD ranging from −53‰ to −75‰, indicating an interacted meteoric fluid origin. Combining the fluid inclusion and stable isotope data illustrates that the main fluorite depositing fluid has characteristics typical of a basinal brine. The authors have no evidence that a magmatic system was involved in the deposit genesis. The proposed model highlights that mineralisation was related to major Mesozoic extensional events coinciding with the gradual opening of the Atlantic and Tethys oceans. In order to account for the chemistry of the fluids, and the siting of the deposits, the authors postulate a genetic relationship with local, continental, evaporite-bearing basins coincident with, and controlled by the E–W fractures.

Multimetallic contamination from Zn-ore smelter: solid speciation and potential mobility in riverine floodbank soils of the upper Lot River (SW France)

The former Zn-ore smelting activity in Viviez (Aveyron, France) resulted in multimetallic contamination of the upper Lot River system (SW France). This study addresses for the first time the metals/metalloids mobility in impacted riverside fluvial soils due to reducing conditions during long-term flooding events. Six impacted riverside fluvio-soils were sampled along the Riou Mort and Lot rivers. Their levels of contamination decrease with the distance from the contamination source. Higher enrichment factors (EF) relative to French average soil metallic content occur 1 km far from the contamination source and vary from 3 for Sn, to 5 for As, 9 for Sb, 27 for Pb, 40 for Zn and 63 for Cd. At 20 km downstream from the contamination source, EF still reach a value of 3 for Cd and Zn. A micro-physical mineralogical characterisation of contaminated soils revealed a variety of metal-bearing phases: metallic compounds, oxides and sulphides, Fe oxides, glass and silicates as well as coke. Sequential chemical extraction experiments were conducted on the most contaminated soil in order to identify which mineral phases were the best candidates to release metals/metalloids. At the end of experiments more than 70 % of total Cd and As, 55 % of Zn and Sb, and 40 % of Pb and Sn were extracted from the soil. Only Cd appeared as readily mobilised, with 33 % of its total amount being extracted in the first steps of experiments. Under reducing conditions, iron oxyhydroxides, franklinite and multimetallic oxides are the best candidates, in decreasing order of importance, for metals/metalloids release from the soil.

Multielementary (Cd, Cu, Pb, Zn, Ni) Stable Isotopic Exchange Kinetic (SIEK) Method To Characterize Polymetallic Contaminations

A new method is proposed to precisely and simultaneously quantify the exchangeable pool of metals in soils and to describe its reactivity at short- and long-term. It is based on multielementary Stable Isotopic Exchange Kinetics (multi-SIEK), first validated by a comparison between two monoelementary radioactive ((109)Cd*, (65)Zn*) IEK experiments, a mono- ((106)Cd) and multi- ((62)Ni, (65)Cu, (67)Zn, (106)Cd, (204)Pb) SIEK. These experiments were performed on a polluted soil located near the Zn smelter plant of Viviez (Lot watershed, France). The IEK results obtained for Cd and Zn were consistent across the experiments. (109)Cd*, (65)Zn* IEK, and multi-SIEK were then applied on 3 non- and moderate impacted soils that also provided consistent results for Cd and Zn. Within these experimental conditions, it can be concluded that no competition occurs between Cd, Zn, and the other metals during SIEK. Multi-SIEK results indicate that the isotopically exchangeable pool of Ni, Zn, and Cu are small (E(Ni), E(Zn), and E(Cu) values up to 17%) whatever the pollution degree of the soils considered in this study and whatever the duration of the interaction. On the contrary, Cd displays the highest E values (from 35% to 61% after 1 week), and E(Pb) displays a maximum value of 26% after 1 week. The multi-SIEK provides useful information on metal sources and reactivity relationship. Ni would be located in stable pedogenic phases according to its very low enrichment factor. The low E(Zn) and E(Cu) are consistent with location of Zn and Cu in stable phases coming from tailings erosion. Though Pb enrichments in soils may also be attributed to tailings particles, its larger exchangeable pool suggests that the Pb-bearing phases are more labile than those containing Zn and Cu. The high mobility of Cd in upstream soils indicates that it has been mostly emitted as reactive atmospheric particles during high temperature ore-treatment.

Fluid inclusion study of the bournac polymetallic (Sb-As-Pb-Zn-Fe-Cu...) vein deposit (montagne noire, France)

Mineralogical studies demonstrate that the Hercynian polymetallic antimony-rich deposit of Bournac can be described by four stages of ore deposition and one of partial ore remobilization. Fluid inclusion data permit calculation of the composition and temperature of the fluids associated with each stage of hydrothermal mineralization and concomitant wall-rock alteration. Stages I and II (Fe-As and Zn) are represented by moderate-salinity H2O-CO2-(NaCl) inclusions which correlate closely with early carbonate deposition. Stage III fluids which are responsible for the deposition of Pb-Sb ores are characterized by low-salinity H2O-(NaCl) inclusions. During the final stage of mineralization (IV), corresponding to the main phase of stibnite deposition, abundant aqueous inclusions confirm the continued involvement of low-salinity fluids and the intense development of potassic clays and secondary silica in the wall rocks. Homogenization temperatures suggest that the whole cycle of mineralization took place during a gradual decrease in fluid temperature of 380°–140°C. Stibnite deposition is restricted to the interval of 230°–140°C thus confirming an essentially epithermal environment. Stage V (partial remobilization) is distinguished by the presence of high-salinity CaCl2-rich inclusions which are tentatively related to Triassic barite mineralization in the region and therefore postdate the Bournac antimony ores. Homogenization temperatures for this stage range 140°–60°C.

Polymetallic pollution from abandoned mines in Mediterranean regions: a multidisciplinary approach to environmental risks

Abandoned mines are a recurrent problem for nearby communities in Mediterranean regions because mine tailings represent a major source of polymetallic contamination. Metal contaminants are emitted in mining areas and dispersed by wind and water erosion in the surroundings. The goal of this literature review was to identify the specific features of polymetallic contamination arising from abandoned mines in the Mediterranean regions. Mediterranean climate conditions and local geochemical context are the most important factors that control the metal-bearing particle dispersion toward the different compartments of ecosystems. Acid mine drainage, as an important source of damage to the environment, is limited to a certain extent by the predominance of carbonate rocks in the Mediterranean regions. In opposite, aeolian contamination is specific to the semiarid conditions of the Mediterranean climate. In this context, impacts on different compartments such as agricultural soils and edible plants or human populations were underlined. The analysis of environmental laws and regulations of North and South Mediterranean countries shows that one of the main differences is the lack of identification and definition of mining waste as a public concern in the latter countries. In order to limit the transfer of contaminants from mining waste to the different components of the environment, phytostabilization of mine tailings was considered as the more adapted green technology even in the Mediterranean region where water access is limited. Finally, this review of polymetallic pollution from abandoned mines in Mediterranean regions enabled to identify priority actions for future research.

Potential of Opuntia ficus-indica for air pollution biomonitoring: a lead isotopic study.

Opuntia ficus-indica (Ofi) is a long-domesticated cactus that is widespread throughout arid and semiarid regions. Ofi is grown for both its fruits and edible cladodes, which are flattened photosynthetic stems. Young cladodes develop from mother cladodes, thus forming series of cladodes of different ages. Therefore, successive cladodes may hold some potential for biomonitoring over several years the local atmospheric pollution. In this study, cladodes, roots, dust deposited onto the cladodes, and soil samples were collected in the vicinity of three heavily polluted sites, i.e., a fertilizer industry, the road side of a highway, and mine tailings. The lead content was analyzed using atomic absorption spectroscopy (AAS) and inductively coupled plasma-mass spectrometry (ICP-MS). Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) was used to characterize the cladode surfaces and the nature of dust deposit, and the lead isotopes were analyzed to identify the origin of Pb. The results show that (i) Ofi readily bioaccumulates Pb, (ii) the lead isotopic composition of cladodes evidences a foliar pathway of lead into Ofi and identifies the relative contributions of local Pb sources, and (iii) an evolution of air quality is recorded with successive cladodes, which makes Ofi a potential biomonitor to be used in environmental and health studies.

Le filon (Zn, F) de Peyrebrune (SW Massif central, France): caractérisation géochimique des fluides au cours du Mésozoïque à la bordure orientale du bassin d'Aquitaine

Fluid inclusion and stable isotope data on the Palaeozoic basement-hosted Peyrebrune (Zn, F) Iodedeposit (Albigeois region), indicate that mineralization originated from circulation of basinal-derived brines during distinct successive Mesozoic extensional events. These new data, set in a regional context, suggest the occurrence of two distinct evaporite-bearing sedimentary basins, now concealed by the Tertiary cover: to the south, an organic matter-rich basin leading to economic Zn-sulfide deposition, and to the north an organic matter-free basin, leading to a small Cu-sulfide deposition. During the fluorite episode, the two basins differentiate by the development of the E-W fracturation: minor in the southern basin, major in the northern one.