Mineralogical Origin Research Articles

Mechanical Properties of Concrete Produced with Coarse Aggregates from Different Mineralogical Origins Using Ultrasonic Tests

The use of nondestructive techniques in the technological control of concrete allows to evaluate and monitor the condition of the material without interfering with its properties; therefore, it is highly desirable in on-site inspections. Among these techniques, ultrasonic testing stands out as one of the most promising by its speed and simplicity to obtain results. However, inferences of strength and stiffness properties using ultrasound parameters should be made with caution, since many factors may interfere with wave propagation. This research aimed to evaluate the behavior of parameters obtained by ultrasonic testing (velocity of wave propagation [V] and stiffness coefficient [C = density × V2]) as predictors of the strength (fc) and stiffness (Eci) of concrete produced with coarse aggregates from different mineralogical origins. To achieve the objective, 128 specimens were produced with four aggregate mineralogical origins and four water-cement ratios, with 8 replications each. The ultrasonic tests were performed with two-frequency transducers (45 and 80 kHz). Prediction models of fc and Eci were statistically significant (P-value < 0,05) for both frequencies. The model using [C] as independent variable present better correlation with Eci (R2 > 91,2%) and with fc (R2 > 82%) than the model using only [V]. General regression models (regardless of the gravel type) were also statistically significant (P-value < 0.05), with R2 > 79% and prediction errors higher than those obtained for the specific models for different rock types.

Effect of aggregate type on the elastic modulus and compressive behavior of concrete: A case study in Colombia

The modulus of elasticity Ec, the specified compressive strength fc', the measured concrete strength, fcr', and the axial strain of the concrete at peak strength εc0 are key parameters for the analysis, design, and construction of reinforced concrete (RC) structures. These parameters require precise laboratory control, which makes routine testing and consistent reporting in the literature challenging. Therefore, in some developing countries, numerical modeling for RC structural analysis relies on results or equations proposed by international building codes as reference values, ignoring the mechanical contribution of locally available materials. This study used five gravel sources from different mineralogical origins in Colombia to evaluate the mechanical properties of twenty concrete mixtures at four water-cement ratios (0.60, 0.55, 0.49, 0.35). Analyses and comparisons of aggregate properties, including mineralogical origins, unit weight, aggregate surface, absorption, and Los Angeles Abrasion Loss (LAAL), are conducted in relation to Ec, fcr', and εc0 and are contrasted against existing literature. Two groups of concrete were defined as normal and high-strength (NS- and HS-concrete), and compressive stress-strain curves were recorded during the tests of 220 cylinders, from which Ec, fcr', and εc0 were obtained. A statistical analysis was conducted to study the main effects and interactions of the aggregate type and water-cement ratio on the modulus of elasticity. It was found that the aggregate type had a significant impact on Ec with no interaction with the water-cement ratio. It led to the development of new expressions to account for the different available aggregates, potentially improving future local building code provisions for Ec. Values of fcr' ranged from 20 MPa to 95 MPa, with the corresponding Ec / √fcr' ratio varying from 4870 to 6140 MPa for the NS-group, while being approximately 25% smaller, on average, for the HS-group. The greatest Ec values are produced by an igneous aggregate type exhibiting the lowest LAAL, while a metamorphic aggregate with 40% LAAL produces the lowest Ec values. However, both aggregates had 100% fractured faces, resulting in the highest fcr' values at 56 days (42 ≤ fcr' ≤ 44 MPa), with the fractured faces of the aggregate being the critical parameter for compressive strength. The εc0 results showed negligible median variations among the aggregate types, except for the aggregate with a smooth surface with fewer fractured faces. Median εc0 values are 0.0019 and 0.0026 for the NS- and HS-group, respectively.

Effects of Particle Size Distribution of Standard Sands on the Physical-Mechanical Properties of Mortars.

Obtained natural sands can present different particle size distributions (PSD), although they have the same mineralogical origin. These differences directly influence the physical and mechanical behavior of mortars and, therefore, the performance of mortar and ceramic renderings. Standardizing the particle size of sands based on pre-established requirements in normative standards (NBR 7214 or ASTM C778) is one way to minimize these effects. However, these standards do not consider the optimization of the granular skeleton through the analysis of bulk density and PSD, which may be insufficient to obtain satisfactory results. Therefore, this paper analyzes the effects of using different particle size ranges on the physical and mechanical behavior of cement and hydrated lime mortars. The properties of consistency index, bulk density, air content, capillary water absorption, water absorption by immersion, flexural strength, compressive strength, and dynamic modulus of elasticity were evaluated. For this purpose, standardized sands of the same mineralogical origin were made with different particle size ranges, being: (i) standardized sand constituted by 25% of coarse and fine fractions (S25-control), (ii) standardized sand constituted by 30% of coarse fraction and 20% of fine fraction (S30-20), and (iii) standardized sand composed by 40% of coarse fraction, and 10% of fine fraction (S40-10), respectively. The results indicated that variations in the particle size composition of the standardized sands are necessary to obtain mixtures with higher compactness and, therefore, mortars with better physical and mechanical performance. Thus, the dosage of the particle size fractions of standardized sand should consider the optimization of the granular skeleton, being the unit mass and the granulometric composition as important parameters to meet this premise.

Mineralogical origin of the chromatic contrast enhancing the Mount Bego petroglyphs (Alpes‐Maritimes, France)

AbstractThe conservation of archaeological heritage such as open‐air petroglyphs is a major challenge due to the vulnerability of surfaces exposed to local environmental conditions. A precise knowledge of their nature therefore constitutes the cornerstone of their preservation. The surfaces of the valleys of the Mount Bego are characterized by a chromatic contrast between the thin red layer covering the outcrops and the underlying greenish substrate, revealed by thousands of prehistoric petroglyphs. To establish the mineralogical nature of the red layer, a spectroscopic, crystallographic, and petrographic study was carried out. Collectively, the results of this study evidence that, unlike rock coatings, this layer formed through the mobilization of structural iron, in the form of Fe (hydr)oxides, from the clay minerals that constitute the rocks. We thus discuss how the succession of events along the geological history of the site has created the environmental conditions for its formation. This study eventually provides useful data on the actual state of the petroglyphs toward their preservation. In a more global context, the conclusions of this study bring insights into the physicochemical mechanism leading to the reddening of recently exposed glacial valleys.

Chemical fractionations and mobility of heavy metals in soils of eastern Uttar Pradesh

In the current investigation, an attempt has been made to assess the various chemical forms and mobility factor (MF) for lead (Pb), cadmium (Cd), chromium (Cr) and nickel (Ni) in four soils of eastern Uttar Pradesh. For this purpose, two different surface soil samples were collected from each of Entisol, Inceptisol, Vertisol and Alfisol soil orders during 2019–20. The modified Tessier sequential extraction procedure was applied to determine the chemical pools of Pb, Cd, Cr and Ni in each soil. Results indicated that total metal content follows the order of Pb&gt;Cr&gt;Ni&gt;Cd across the orders, whereas mobility factor of micronutrients could be arranged as: Cd&gt;Pb&gt;Ni&gt;Cr. The bioavailable metal fraction of all micronutrients, i.e. exchangeable pool (F1) was maximum in Inceptisol. The highest carbonate bound (F2), Fe–Mn oxides bound (F3), organically bound (F4) and residual (F5) fraction were recorded in Vertisol, Alfisol, Inceptisol and Alfisol, respectively for all heavy metals. The mean percentage value of Pb and Ni fractions were in the order of F5&gt;F3&gt;F4&gt;F2&gt;F1, whereas Cd whose chemical fractions follows the order of F2&gt;F3&gt;F4&gt;F5&gt;F1. The Pb was highly mobile in Vertisol, Ni in Inceptisol, while Cd and Cr in Entisol. Therefore, availability and mobility of heavy metals in the soil environment depends mainly on their association with various chemical fractions of the soil which relies on the mineralogical origin of the metals.

Carbonation of model cement pastes: The mineralogical origin of microstructural changes and shrinkage

This study explored the reactive processes of atmospheric carbonation and the consequences with respect to cementitious materials. Two model pastes were used: hydrated C3S (including C-S-H and portlandite) and a paste prepared by hydrating a blend of C3S and nanosilica (including C-S-H only). The two pastes were carbonated under accelerated conditions in the laboratory. The resulting mineralogical assemblage was examined using X-ray diffraction, thermogravimetric analysis and nuclear magnetic resonance. The microstructural changes were studied by X-ray tomography and porosimetry, and their macroscopic impacts were evaluated through gas diffusion and shrinkage measurements. The use of model pastes allowed for the evaluation of the change in solid volume induced by the carbonation of C-S-H. C-S-H decalcification and subsequent silica chain polymerisation were found responsible for carbonation shrinkage (and potentially cracking). Finally, the results highlight the protective role of portlandite: portlandite helped in limiting C-S-H decalcification and then reducing carbonation shrinkage and cracking.

Diagenesis of Vera Rubin Ridge, Gale Crater, Mars, From Mastcam Multispectral Images.

Images from the Mars Science Laboratory (MSL) mission of lacustrine sedimentary rocks of Vera Rubin ridge on “Mt. Sharp” in Gale crater, Mars, have shown stark color variations from red to purple to gray. These color differences crosscut stratigraphy and are likely due to diagenetic alteration of the sediments after deposition. However, the chemistry and timing of these fluid interactions is unclear. Determining how diagenetic processes may have modified chemical and mineralogical signatures of ancient Martian environments is critical for understanding the past habitability of Mars and achieving the goals of the MSL mission. Here we use visible/near‐infrared spectra from Mastcam and ChemCam to determine the mineralogical origins of color variations in the ridge. Color variations are consistent with changes in spectral properties related to the crystallinity, grain size, and texture of hematite. Coarse‐grained gray hematite spectrally dominates in the gray patches and is present in the purple areas, while nanophase and fine‐grained red crystalline hematite are present and spectrally dominate in the red and purple areas. We hypothesize that these differences were caused by grain‐size coarsening of hematite by diagenetic fluids, as observed in terrestrial analogs. In this model, early primary reddening by oxidizing fluids near the surface was followed during or after burial by bleaching to form the gray patches, possibly with limited secondary reddening after exhumation. Diagenetic alteration may have diminished the preservation of biosignatures and changed the composition of the sediments, making it more difficult to interpret how conditions evolved in the paleolake over time.

Assessing Geoavailability of Zinc, Copper, Nickel, Lead and Cadmium in Polluted Soils Using Short Sequential Extraction Scheme

ABSTRACT An attempt has been made to assess the geoavailability of heavy metals in polluted soils using short sequential fractionation schemes. For this purpose, 25 composite soil samples were collected from various locations (across India) of which had a history of receiving sewage sludge, municipal solid waste, polluted river water and industrial effluents. Four composite soil samples were also collected from adjacent fields which had not received contaminated amendments. Zinc (Zn), copper (Cu), nickel (Ni), lead (Pb) and cadmium (Cd) were extracted from the soil solution plus exchangeable, carbonate bound, Fe and Mn oxides bound, and organic matter bound fractions. Copper (53.0%) was largely adsorbed by the organic fractions, while a significant amount of Zn (56.6%), Ni (78.4%), Pb (57.4%), and Cd (59.7%) was extracted from the Fe/Mn oxide bound fraction. Regression analysis revealed that water-soluble plus exchangeable pool of Zn, Cu, Ni, Pb and Cd contributed positively towards the uptake of these elements by spinach and wheat under pot experiment. Behaviour, transport and the ultimate fate of heavy metals in the soil environment depend largely on their association with different geochemical fractions of the soil which is related to the mineralogical origin of the metals.

Clay Mineralogical Characteristics and Origin of Sediments Deposited during the Pleistocene in the Ross Sea, Antarctica

Clay Mineralogical Characteristics and Origin of Sediments Deposited during the Pleistocene in the Ross Sea, Antarctica

Origin of Long‐Wavelength Magnetic Anomalies at Subduction Zones

AbstractMost subduction zones have associated long‐wavelength anomalies in the lithospheric magnetic field observed at satellite altitude. We model the 13 subduction zones defined by seismicity and seismic tomography using vertically integrated magnetizations that are increasing, level, or decreasing away from the trench. These mimic end members of a magnetized mantle wedge, a uniform layer, and a magnetized dipping lithospheric slab. They are added to a global model of vertically integrated magnetization based on continental and oceanic geology. We find the dipping slab places the anomaly too close to the trench, while the other two fit the data equally well and use the level model in the main part of the study. Anomalies at the Sunda, Aleutians, Cascadia, Central American, and Kamchatka‐Japan zones are well modeled by uniform magnetization of differing susceptibilities and spatial extents. We show the South American anomaly is weak because the magnetization lies mainly in the null space that produces no external potential magnetic field. There is no anomaly associated with the Ryukyu system, possibly because the present subduction started too recently for magnetization to have formed. The magnetic anomaly stretching down the Baja California peninsula is not present in the prediction because there is no seismicity on which to base a slab geometry, but recent tomography suggests a fossil slab there and we propose historic subduction as the origin of the Baja magnetic anomaly. Finally, we discuss the mineralogical origins of the magnetization and favor serpentinization of the region above the subducted plate.

Evaluation of the elemental distribution in soil samples collected from ship-breaking areas and an adjacent island

Ship-breaking yards in the world mostly reside along the coastal areas which possess diverse elemental contents due to the presence of heavy minerals. So to explain the heavy elemental enrichment of ship-breaking sites in terms of only anthropogenic contribution is insufficient. While studying elemental distribution of ship-breaking sites, choosing appropriate control sample is vital. To evaluate the elemental distribution in ship-breaking yards of Bangladesh and in an adjacent island (Sandwip), soil samples from each site and some heavy minerals have been analyzed for Na, K, Sc, Cr, Fe, Co, As, Sb, Cs, La, Ce, Sm, Hf and Th abundances by neutron activation analysis. For assessing elemental distribution, pollution load index (PLI), geo-accumulation index and inter-element correlation study were performed. Co-related variation of Cr and Fe (r = 0.651) and chemical compositions of heavy minerals invoke that a significant portion of elemental enrichment in ship-breaking yards seems to have mineralogical origin while the enrichments of As, Sb and Cs (mean abundances: 11.3 ± 3.9, 5.66 ± 4.97 and 10.9 ± 6.6 ppm, respectively) are solely originated from anthropogenic activities (e.g., ship-breaking). On the other hand, elemental distribution of Sandwip (which is sometimes used as control sample) seems to be unaffected by the mainland ship-breaking activities and possesses crustal origin, though a minute fractionation of heavy metals is observed within the east (PLI: 0.84 ± 0.05) and west (PLI: 0.52 ± 0.04) side of the island. For the first time, this study reveals the mineralogical contribution of heavy elements in ship-breaking site and will be decisive for choosing proper elemental abundances of control site.

Seismological Constraints on the Small‐Scale Heterogeneity in the Lowermost Mantle Beneath East Asia and Implication for Its Mineralogical Origin

AbstractPrevious seismological studies have focused on the large‐scale heterogeneity of the D″ layer beneath East Asia. Here, we use high‐frequency PcP precursors recorded at dense networks in China and Japan to constrain the small‐scale heterogeneity in this region. By forward modeling of the stacks of recorded PcP precursory signal, we find that the small‐scale heterogeneity in the D″ layer beneath East Asia is characterized by a P wave velocity perturbation of 0.1‐0.2% and a dominant length scale of 4‐20 km. Although the resolved length scale is similar to the dimension of the subducted oceanic crust, the weak velocity perturbation is difficult to explain by basaltic rock in the lowermost mantle. Postperovskite transition of the supposed slab might also not be viable for generating weak heterogeneity; thus, new explanations are needed from geodynamics and mineral physics to account for the different strength of the large‐ and small‐scale heterogeneity.

Paleoenvironmental reconstruction of the semi-arid Chaco region of Argentina based on multiproxy lake records over the last six hundred years

In this paper, we analyze the paleoclimatic and paleoenvironmental evolution of Laguna Yema in semi-arid Chaco region of Argentina over the past six hundred years. High resolution multiproxy studies of lake sediments utilize analyses of lithology, mineralogy, geochemistry, palynology, and are constrained by radiocarbon and gamma spectrometry dating. Laguna Yema sediments were mainly composed of well stratified fine sediments (silts and clays), with variable proportions of quartz, clays (illite) and feldspar (microcline and albite). Twelve light and heavy geochemical elements were registered. Most elements (Al, Si, K, Ti, Fe, Rb, Ba, and Br) are associated with illite and albite. Different material transport processes related to the changes in aridity and humidity of the basin were identified using the main mineralogical origins of geochemical elements. Palynological records indicate cycles of contraction and expansion of the lake, with an increase in concentration of Alternanthera aquatica during wet periods (expansion of lake), and an increase in Ambrosia, Poaceae and fern spores during dry periods (contraction of lake). These changes are linked to fluctuations in moisture conditions in the Subandean Mountains and semi-arid Chaco regions, in response to interactions between the South American Monsoon System (SAMS) and the South American Low Level Jet (SALLJ), which send warm and humid air to northern Argentina. In a regional context, the Laguna Yema records are in accordance with the analyses of the temporal and spatial pattern of moisture distribution for the last six centuries.

Soil diagnosis of an urban settlement with low levels of anthropogenic pollution (Stepnoe, Saratov region)

A soil diagnosis of an urban territory Stepnoe (Saratov region) was conducted within the framework of soil research monitoring of inhabited localities with low levels of anthropogenic impact using chemical and microbiological analysis. Excess over maximum permissible concentration (MPC) of mobile forms of Cr, Zn and Cd were not observed within the researched territory. A universal excess over MPC of mobile forms of Ni, Cu and Pb was established which is most likely connected with anthropogenic contamination. It was discovered that, at the territory of the Stepnoe settlement, mobile forms of heavy metals compounds (HM) in most cases formed paragenetic associations with high correlation coefficient and despite this, an excess over MPC was not significant. This point to a common mineralogical origin of the elements inherited from the parent rock. The values of the total index of chemical contamination were not above 16, which puts the researched samples in a category with permissible contamination. The indices of the total number of heterotrophic bacteria, iron-oxidizing and hydrocarbon-oxidizing bacteria in most samples corresponded to normal indices for chestnut solonetsous and saline soils. In some samples, a deviation from the normal indices was observed justifying the impact of specific contaminants on the soil.

The mineralogical origin of calcium pyrophosphate dihydrate and carbonate hydroxyapatite depositions in human ligamentum flavum

Calcification of ligamentum flavum (CLF) in cervical spine was characterized in terms of crystal morphology, mineral phases and chemical components. The cause of the disease, forming mechanism, as well as the developing process of the calcification were discussed combined with the pathological results. Micro-FTIR, Raman, scanning electron microscope (SEM), transmission electron microscope (TEM) and synchrotron radiation X-ray diffraction (XRD) were applied to two cases of CLF in cervical spine. The results showed that the calcification mainly presented four kinds of morphology, i.e., columnar, granular, flocculent and spherical. Columnar and granular calcification, which was constituted by single crystals with good crystalline shape and sharp boundary, was identified as triclinic-calcium pyrophosphate dihydrate (t-CPPD). Flocculent or spherical calcification, which was aggregated by nano-polycrystalline, was mainly composed by B-type carbonate hydroxyapatite. The results of micro-FTIR and Raman showed that CPPD and CHA unevenly distributed among the calcification aggregates, where the proportion of CHA decreased but CPPD increased from the center to the periphery. Based on the above analysis, we estimated that granular and columnar CPPD crystals were formed in the initial stage of calcification . In the later stage, the decomposition of CPPD and deposition of CHA occurred on the calcification aggregates, in which the former process provided the material source for CHA formation. During the deposition of CHA, nanocrystals firstly formed, followed by their aggregation into flocculent calcification, and finally forming spherical calcification.

Identification of inorganic and organic inclusions in the subglacial antarctic Lake Vostok ice with Raman spectroscopy

The investigation of inclusions entrapped into the accretion ice of the subglacial Lake Vostok in Antarctica gives an insight into former times of the Antarctic history. Terrestrial (of biological and geologically mineralogical origin) as well as extraterrestrial (meteorites) materials are hermetically embedded in the Vostok ice core and provide information about the conditions and events on Earth existed/occurred during last million years. Confocal Raman spectroscopy is well suited for the analysis of the inclusions without melting the ice and, therefore, preventing undesirable contamination with present‐day material. It is a nondestructive method for material identification with depth resolving capability. It permits a locally precise statement about the chemical–mineralogical composition and allows the context information preservation of several side by side inclusions.Here, we present first results of our Raman measurements of the inclusion embedded in the Lake Vostok ice sample 5G‐3 3607‐4 (3607‐m depth). The results obtained confirm that Raman spectroscopy is a very useful method for the exploration of inclusions entrapped into lattice of any natural ice. As Raman spectroscopy is already planned to be applied in upcoming missions in space research (ExoMars, Mars 2020, to the icy moons), a co‐operation of the space science community with the Antarctica–Lake Vostok community is suggested to test the space instrumentation under the extreme environment of the Central East Antarctica and conditions of the subglacial Lake Vostok. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Quaternary evolution of the rivers of northeast Hainan Island, China: Tracking the history of avulsion from mineralogy and geochemistry of river and delta sands

The mineralogy and geochemistry of sands were investigated in the Nandu and Wanquan rivers, Hainan Island, China, to determine the history of avulsion in the lower reaches of the Nandu River. The study also provided the opportunity to assess the utility of geochemical analysis of sands as a provenance tool. Much of the heavy mineral fraction in the rivers consists of subangular Fe-Ti oxide and Fe-(hydr)oxide minerals, and less stable minerals such as amphibole, epidote, and andalusite, whereas rounded resistant ilmenite, rutile, tourmaline and zircon predominate on the deltaic coast. Mineral assemblage and chemical composition of individual samples are related to specific source areas and river tributaries. The results demonstrate northwestwards flow of the Nandu River during the mid-Holocene and earlier avulsion of the river to the northeast coast, probably during a Late Pleistocene marine highstand. Minor basement tilting, producing little relief, was sufficient to divert the lower reaches of rivers, and this effect was enhanced where basalt flows dammed former river courses. Bulk sample REE geochemistry is largely controlled by the relative abundance of monazite, allanite, titanite, zircon and epidote, derived principally from granites. Detrital geochemistry alone shows too much variability to interpret provenance. However, a smaller number of heavy mineral analyses provide an understanding of the mineralogical origins of geochemical variation, thus enabling interpretations of provenance.

Chemical availability of arsenic and heavy metals in sediments from abandoned cinnabar mine tailings

The understanding of the solid-phase speciation of arsenic in soils and sediments is important in the evaluations of its potential mobility and availability in the environment. The spoil heaps of abandoned mercury mines contain waste materials with high arsenic and heavy metals concentrations. The weathering of these tailings can cause their mobilization to the surroundings. In this work, the mobility and availability of arsenic and some heavy metals were evaluated in sediments from two heavily polluted mercury mining districts in Asturias (NW Spain). For this purpose, a slightly modified version of the Bureau Community of Reference sequential extraction scheme was applied to sediments. The total contents in the operationally defined fractions were analysed by inductively coupled plasma-atomic emission spectrometry. Extremely high total arsenic concentrations were found in all sediments ranging from 4,000 to 24,800 mg kg−1. High easily mobilizable arsenic contents were found in the first mining area, related to the solubilization of Ca-bearing phases, supported by extracts analyses, X-ray diffraction results and the positive correlation found among the As and Ca fractionations. Ni and Zn were the most mobile among heavy metals, being Cr the least mobile, suggesting an anthropogenic origin due to the metallurgical processes, transport or dispersion generated from neighbour spoil heaps. In the second mining area, the bulk of As was concentrated in the residual phase, as well as Cr, Cu, Fe, Pb, Ti, indicating a mineralogical origin and the low availability of these elements. The strong correlations established between As and Fe and Ti distributions support the hypothesis that As is mainly associated to structural mineral phases in these sediments.

Mineralogy and chemistry of the green stone artifacts (muiraquitãs) of the museums of the Brazilian State of Pará

Muiraquitãs, lithic artifacts found in the Amazon basin, have been considered to be Asian in origin, or to have been sculpted by the legendary female Amazon warriors. These pieces are now very rare, and are found mainly in museum collections. In the present study, the mineralogical and chemical content of 23 specimens from the collections of the Museu de Gemas (Gemstone Museum) and Museu do Encontro (Meeting Museum) in Belém, Brazil, were analyzed. Most of the pieces were made of minerals commonly found in Brazil - quartz, albite, microcline, variscite, anorthite, and tremolite (the equivalent of nephritic jade). However, four of the pieces were made of jadeite, that is, jadeitic jade, which is unknown in the Amazon basin or in other parts of Brazil. The confirmation of the presence of this mineral in some of the artifacts reopens the debate on the mineralogical origin of the muiraquitãs found in the Amazon basin. Before the present discovery, their origin was defended as Amazonian due to the absence of jadeite jade in the searched pieces and the fact that jadeite was not found in Brazil but in Central America and Asia.

Characterizing Abandoned Mining Dams by Geophysical (ERI) and Geochemical Methods: The Linares-La Carolina District (Southern Spain)

The mining exploitation of metallic sulphides, together with the activities associated to the mineral treatment and smelting, when maintained through centuries due to the wealth of the ores, generate important accumulations of wastes in structures of different kind of tailing dams and ponds, for instance. When no previous corrective steps are taken, as usually happens in old exploitations, this means a serious risk of environmental pollution, due to the mobilisation of heavy metals. The present study has been carried out in a mining district, actively exploited during the last two millennia, that was the first world’s producer of lead during some periods (Linares-La Carolina, southern Spain). In this district, the mining activity was associated to a philonian network of metallic sulphurs and ended by the 1980s of the past century. The ancient mining operations, mostly subterranean, have generated large accumulations of residues without any prior corrective action. Therefore, this work intends to characterise these mining dams and determine the influence of these mining wastes on the quality of surface and ground waters. With this goal, three structures that store the mining refuse of different mineralogical origin have been selected. First, a geochemical characterisation of the soil was performed in the area surrounding each of the structures. In all cases, high levels of trace elements (including Pb, Zn, Cu, Cd, Mn, As, Sb and Ba) were observed. A hydrochemical study revealed the mobilisation through the aqueous medium of certain contaminants from the leachate of these ancient accumulations; these contaminants will flow to the streams that drain the area or to the aquifers of the sector. The internal characterisation of these structures was performed with geophysical techniques, specifically electrical resistivity imaging (ERI). The six generated resistivity models have allowed the identification of the morphology of the structures, variations in the vertical and horizontal distribution of the deposited material, fracture zones, water content and reload–unload zones and the contact of the mining wastes with the substrate. Thus, the ERI study confirms the lack of impermeabilisation measures for the terrain in the spill zones in all three cases, which indicates a high risk of contamination of the soil and waters. The obtained images also permit the identification of the ideal positions to conduct future borehole controls.