Geoavailability of Ni, Cu, Zn, As, Cd, and Pb in the Sierra de Cartagena – La Unión (SE Spain)

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UNIVERSIDAD POLITÉCNICA DE CARTAGENA

Departamento de Ingeniería Minera, Geológica y Cartográfica

Tesis doctoral presentada por:

Luis Alberto Alcolea Rubio

Geoavailability of Ni, Cu, Zn, As, Cd, and Pb in the Sierra de Cartagena – La Unión (SE Spain)

Directores:

Dr. Roberto L. Rodríguez Pacheco Dr. Isidro J. Ibarra Berrocal

Mayo de 2015

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The development of this thesis has been possible with the Research Funding source of Seneca Foundation of Murcia, Spain, Project PB/44/FS/2002.

The author gratefully acknowledges the infrastructural support of the Assistance Service for Technological Research (Servicio de Apoyo a la Investigación Tecnológica, SAIT) of the Universidad Politécnica de Cartagena (Spain), where all the experimental analyses were performed.

Logic will get you from A to B.

Imagination will take you everywhere.

—A. Einstein (1879–1955)

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CONTRIBUTIONS RESULTING FROM THIS RESEARCH

 Alcolea, A., Ibarra, I., Caparrós, A., Rodríguez, R., 2010. Study of the MS response by TG–MS in an acid mine drainage efflorescence. Journal of Thermal Analysis and Calorimetry 101, 1161–1165.

Research category: Analytical chemistry Quartile in category: Q3 (2010)

Impact factor: 1.752 (2010)

 Alcolea, A., Vázquez, M., Caparrós, A., Ibarra, I., García, C., Linares, R., Rodríguez, R., 2012. Heavy metal removal of intermittent acid mine drainage with an open limestone channel. Minerals Engineering 26, 86–98.

Research category: Mining and mineral processing Quartile in category: Q2 (2012)

 Alcolea, A., Fernández-López, C., Vázquez, M., Caparrós, A., Ibarra, I., García, C., Zarroca, M., Rodríguez, R., 2015. An assessment of the influence of sulfidic mine wastes on rainwater quality in a semiarid climate (SE Spain). Atmospherical Environment 107, 85–94.

Research category: Environmental sciences Quartile in category: Q1 (2013)

 Alcolea, A., Caparrós, A., Rodríguez, R., 2015. Seawater analysis in wadi outlets surrounding the Sierra de Cartagena – La Unión. Oral presentation at the Workshop on Post-Mined Polluted Landscapes: Risks and Reclamation Techniques, April 22–24. Universidad Politécnica de Cartagena (Spain). LIFE 09 ENV/ES/000439 + MIPOLARE Project.

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CONTENTS

Acknowledgements ...i

Summary ... ii

Resumen ... iii

1. Introduction ... 1

1.1. Trace-element pollution ... 4

1.2. Geoavailability ... 5

1.3. Mobility ... 6

1.4. Solubility ... 6

1.5. Metal speciation ... 7

1.6. Exposure ... 8

1.7. Bioavailability ... 8

1.8. Toxicity ... 9

2. Objectives and Working hypotheses ... 11

2.1. Overall aim ... 13

2.2. Partial aims ... 13

2.3. Working hypotheses ... 14

3. Literature review ... 15

3.1. Geological setting ... 17

3.2. Mining heritage ... 17

3.3. Geophysics and geotechnical engineering ... 18

3.4. Mining and metallurgical wastes ... 18

3.5. Soil and sediment pollution ... 18

3.6. Pollution of continental waters ... 19

3.7. Mar Menor and surrounding protected landscapes... 19

3.8. Environmental remediation and ecological restoration ... 19

4. Characterization of the study area ... 21

4.1. Geographical location and landscape relief ... 23

4.2. Surface water and groundwater hidrology in the Sierra Minera ... 24

4.3. Climatology ... 25

4.4. Soils and vegetation ... 25

4.5. Geologic setting ... 29

4.6. Mineral deposits ... 30

4.7. Mining activity ... 31

4.8. Metallurgical processes ... 32

5. Sampling methods ... 35

5.1. Rainwater ... 37

5.1.1. Hellmann rain gages ... 39

5.2. Surface runoff ... 42

5.2.1. Wadis hydrology ... 43

5.2.2. Timeline ... 46

5.3. Groundwater ... 49

5.3.1. Springs hydrology ... 50

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5.4. Seawater ... 52

5.4.1. Sampling design ... 52

5.5. Efflorescences ... 54

5.6. Types of mining and metallurgical wastes ... 56

5.7. Lithological types ... 61

5.7.2. Classification criteria ... 62

6. Analytical methods ... 73

6.1. Liquid specimens ... 75

6.1.1. pH and EC ... 75

6.1.2. Ion chromatography ... 76

6.1.3. Inductively coupled plasma – mass spectrometry ... 78

6.2. Solid specimens ... 80

6.2.1. Thermogravimetric analysis ... 81

6.2.2. CHN analysis ... 82

6.2.3. Wavelength dispersive X-ray fluorescence ... 85

6.2.4. X-ray diffraction ... 86

7. Results ... 91

7.1. Rainwater characterization ... 93

7.1.1. Data summary ... 93

7.1.2. Plastic rain-gauges ... 102

7.1.2.1. Data summary and total deposition fluxes ... 102

7.1.2.2. Temporal evolution of some parameters ... 106

7.1.2.3. Estimates of natural versus anthropogenic analysis ... 108

7.1.2.3.1. Correlation matrices ... 108

7.1.2.3.2. Principal component analysis ... 113

7.1.2.3.3. Enrichment factors ... 116

7.2. Runoff water characterization ... 117

7.2.2. Runoff quality analysis for irrigation and other domestic or industrial uses ... 127

7.2.3. Ficklin diagram ... 130

7.2.4. Seasonal variation of parameters at B1 and G1 ... 131

7.2.5. Correlation matrices for physical and chemical parameters at B1 and G1 ... 135

7.2.6. Principal component analysis for major ions and heavy metals at B1 and G1 ... 138

7.3. Groundwater characterization ... 138

7.3.2. Analysis of springwater quality for irrigation and other domestic or industrial uses ... 143

7.3.3. Springwater geochemistry ... 146

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7.3.4. Ca/Mg molar ratios ... 148

7.3.6. Temporal evolution of some physico-chemical parameters ... 150

7.3.7. Connection between Tomasa open-pit mine and Barranco del Moro spring ... 156

7.3.8. Correlation matrices ... 157

7.3.9. Principal component analysis ... 160

7.4. Seawater characterization ... 163

7.5. Efflorescences characterization ... 169

7.5.1. Stereo microscopic observation ... 173

7.5.3. Compositional analysis by WDXRF ... 175

7.5.4. Structure determination by XRD ... 177

7.5.5. Enrichment of metals in salt efflorescences ... 179

7.5.6. Leaching test ... 179

7.5.8. Correlation matrix ... 183

7.6. Characteristics of the different types of mine and metallurgical wastes ... 187

7.6.5. Enrichment of metals in mine and metallurgical wastes ... 193

7.7. Characteristics of the different lithological types ... 199

7.7.1. Stereo microscopic observation ... 201

7.7.6. Enrichment of metals in lithological types ... 214

8. Discussion ... 223

8.1. Geoenvironmental model of the mineral deposits in the Sierra Minera de Cartagena – La Unión ... 225

8.1.1. Deposit micro-fraction geochemistry ... 225

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8.1.2. Drainage signature ... 226

8.2. Geochemical cycles of Ni Cu, Zn, As, Cd, and Pb in the Sierra Minera and Campo de Cartagena ... 229

8.2.1. Geochemical cycles of trace metals in the Sierra Minera ... 229

8.2.2. Geochemical cycles of trace metals in the Campo de Cartagena ... 232

8.3. Geoavailable heavy-metal mass balance for Mar Menor lagoon ... 232

8.3.1. Minimal Risk Levels and trace-metals uptake ... 236

9. Conclusions ... 239

9.1. Partial findings ... 241

9.1.1. Rainwater ... 241

9.1.2. Surface runoff ... 241

9.1.3. Groundwater ... 242

9.1.4. Seawater ... 242

9.1.5. Efflorescences ... 242

9.1.6. Types of mining and metallurgical wastes ... 243

9.1.7. Lithological types ... 244

9.2. Overall finding ... 244

9.3. Future research ... 246

10. References ... 247

11. Appendix ... 259

11.1. Appendix 1. Paper 1 ... 261

11.2. Appendix 2. Paper 2 ... 269

11.3. Appendix 3. Paper 3 ... 285

11.4. Appendix 4. Data sheets for weather stations... 307

11.5. Appendix 5. Data sheets for sampling positions of runoff water ... 325

11.6. Appendix 6. Data sheets for sampling positions of groundwater ... 345

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ACKNOWLEDGEMENTS

Everything started a distant afternoon in 2004, while I was attending a SEM user.

Roberto entered the laboratory and another researcher—José Matías—introduced me to him. Roberto told me—in the most persuasive way—that he was looking for someone to perform some simple fieldwotk related to rainwater in the Campo de Cartagena. Since then, he became my supervisor. That simple fieldwork finally lasted 5 long years. Not only rainwater, but also surface runoff, springwater, seawater, efflorescences, mine wastes, and lithotypes were added to the study. Sampling labours totalized 126 field trips, covering a distance of at least 9784 km with my tough and hard-wearing vehicle.

I am grateful to Roberto, for his enthusiastic spirit in guiding me across the research jungles in which I entered, unwary and ignorant; Cristóbal García, for being my constant compass in the knowledge of the Sierra Minera; José Ángel Rodríguez, for his geological wisdom; José Ignacio Manteca, Marisol Manzano, Concepción Martínez, Víctor León, Carmen Fernández, and Mathieu Kessler for clarifying my doubts when I felt at a crossroads.

Half the work has been possible by the people in charge of every weather station:

Áurea Martínez (El Algar), José Constanzo (Cabo de Palos), Isabel Gallego and Manuel Urrea (Corvera), Fernando Blaya (La Pinilla), José Moreno (Fuente Álamo), Carmen Moreno (Balsapintada), Lorenzo López and Jesús Conesa (Los Martínez del Puerto), José Castillo (La Tercia), Angelita Benzal (Pozo Estrecho), Juan María Fernández (Torre- Pacheco), Juan Manuel Gómez (Torreblanca), Mariano García (Avileses), and Francisco García (Sucina). They and their families had an endless patience, being very nice and attentive with me.

I am deeply indebted to Ana María, who has been and continues to be with me every step of the way. She is a relentless goddess with an overwhelming practicality. I’m the yin and she’s the yang. She loves to argue about the smallest things but is an outstanding collaborator. I’m a lucky man.

Many other people also participated with me throughout the years of field trips: Virma Robles, Ana Vanessa Caparrós, Gerald Dany, Desi (nearly a person), Germán Paniagua, Emma Romero, Carlos De Coig, Cristina Guerrero, and Juan Ríos. They all explored on foot the vast and untamed landscape and were surprised—like me—to see so much beauty beyond mining wastes and a depleted orography. Nature always forgives.

Thanks to the SAIT staff (my second home, or the first one, according to my wife):

Isidro, my co-supervisor, who has facilitated the tasks in spite of my split work days; Ana Belén, Magdalena, and Ana Vanessa, who analyzed most of the samples; Juan Antonio, who helped me to install the plastic rain gauges; María José and Vicente, examples of dedication, commitment, and hard work; Lola, who helped me with some drawings and maps; Luis Pedro, María, and David, who were also excellent working companions.

Last but not least, thanks to the people that shape the emotional environment in which I live: Ana María, Virginia and Miguel, Ana Vanessa and Pablo, Paula, David, my parents, brother, sister, other family members, friends, and components of Torre Nazaret’s project.

This work is the ten-year gift of life that they deserve.

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SUMMARY

The aim of this thesis was to contribute to the interpretation of the geogenic and anthropogenic factors, at local (hydrographic basin) and regional levels, that control the geoavailability (solubility and mobility) of Ni, Cu, Zn, As, Cd, and Pb in the Sierra Minera de Cartagena – La Unión, as well as to evaluate the influence of the abandoned mining landscape on the Campo de Cartagena and Mar Menor lagoon. The study period extended from 2003 to 2012.

Across the large plain of 1600 km² that forms the Campo de Cartagena, 15 weather stations were monitored to collect 920 rainwater samples. In addition, 179 surface runoff water samples were gathered in 13 ephemeral watercourses, 127 springwater samples in 5 springs, 16 seawater samples in 8 wadi outlets, 15 efflorescent sulfate salts, 7 types of mine wastes, and 23 types of parent materials. The assessment of such variety of specimens helped to understand the mechanisms that make Ni, Cu, Zn, As, Cd, and Pb geoavailable in the Sierra Minera of Cartagena – La Unión. For this purpose, these trace elements were studied in the geological context, taking into account their geochemical cycles, the different types of mining and metallurgical wastes present in the derelict mining site, and the sphere of influence to the bordering areas.

Geoavailability of trace elements depends on the speciation of its soluble phases, which is affected by geochemical, hydrogeological, biological, and anthropogenic (mining, agricultural, and industrial activities) parameters. Knowledge of the geoavailability of metals in soils, its transfer mechanism to plants and other organisms, as well as the risk to public health remain key issues. This doctoral thesis wishes to tackle these problems with the most advanced instrumental techniques. Liquid samples were evaluated through the determination of pH, Electrical Conductivity (EC), major ions by Ion Chromatography (IC), and the metals of interest by Inductively Coupled Plasma – Mass Spectrometry (ICP–MS). The physico-chemical characterization of the solid samples involved its stereo microscopic observation, the determination of the structure by X-Ray powder Diffraction (XRD), the compositional analysis by Wavelength Dispersive X-Ray Fluorescence spectrometry (WDXRF), CHN analysis, and ThermoGravimetric analysis coupled to Mass Spectrometry (TG–MS).

Furthermore, the leaching test DIN 38414-S4 was performed over the solid specimens to appreciate the hazard and potential mobility of the different analytes. pH, EC, major ions and several metals (Ni, Cu, Zn, As, Cd, Sb, and Pb), were measured in the leachate samples.

The results have confirmed that geoavailability of trace metals in the Sierra Minera is governed by physico-chemical weathering of mining and metallurgical wastes, as well as by the oxidation of metallic sulfides associated to the Pb-Zn ores. Regarding the transport, dispersion, and deposition mechanisms of Ni, Cu, Zn, As, Cd, and Pb, the geoavailable trace-metal mass balance for Mar Menor lagoon disclosed that aeolian erosion transfered 81% of the overall input of metal pollutants coming from the Sierra Minera, groundwater input contributed 16%, and watershed stream input only represented 3%. This proved that scattering of those trace elements is NOT controlled by continental water bodies (surface runoff and groundwater).

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RESUMEN

El objetivo de esta tesis es contribuir a la interpretación de los factores geogénicos y antropogénicos, a escalas local (cuenca hidrográfica) y regional, que controlan la geodisponibilidad (solubilidad y movilidad) de Ni, Cu, Zn, As, Cd, and Pb en la Sierra Minera de Cartagena – La Unión, así como evaluar la influencia del paisaje minero abandonado sobre el Campo de Cartagena y el Mar Menor. El período de estudio se extendió desde 2003 hasta 2012.

Se recogieron 920 muestras de agua de lluvia en las 15 estaciones pluviométricas repartidas por la gran llanura de 1600 km² que constituye el Campo de Cartagena. Además, el estudio de campo se complementó con 179 muestras de agua superficial recogidas en 13 ramblas, 127 muestras de agua subterránea recogidas en 5 manantiales, 16 muestras de agua de mar recogidas en 8 desembocaduras de ramblas, 15 especímenes de eflorescencias de sulfatos, 7 tipos de residuos mineros y 23 tipos de rocas. La evaluación de tal variedad de muestras ayudó a comprender los mecanismos que hacen geodisponibles estos metales en la Sierra Minera de Cartagena – La Unión. Dichos elementos traza se estudiaron en su contexto geológico, teniendo en cuenta sus ciclos geoquímicos, los diferentes tipos de residuos minero-metalúrgicos presentes en esta zona minera abandonada y la esfera de influencia hacia las áreas circundantes.

La geodisponibilidad de los elementos traza depende de la especiación de sus fases solubles, la cual se ve afectada por parámetros geoquímicos, hidrogeológicos, biológicos y antropogénicos (actividades minera, agrícola e industrial). El conocimiento de la geodisponibilidad de los metales en el suelo, su mecanismo de transferencia a la biota y el riesgo para la salud pública, continúan siendo cuestiones clave a abordar. La presente tesis doctoral trata de evaluar estos problemas con ayuda de las técnicas instrumentales más avanzadas. Las muestras líquidas se evaluaron mediante la determinación del pH, Conductividad Eléctrica (CE), iones mayoritarios por Cromatografía Iónica (CI) y los metales de interés por Espectrometría de Masas de Plasma Acoplado Inductivamente (EM–PAI). La caracterización fisicoquímica de las muestras sólidas se llevó a cabo mediante observación estereomicroscópica, determinación de su estructura mediante Difracción de Rayos X (DRX), análisis composicional por espectrometría de Fluorescencia de Rayos X por Dispersión de Longitud de onda (FRXDL), análisis CHN y Análisis TermoGravimétrico acoplado a Espectrometría de Masas (ATG–EM). Además, sobre las muestras sólidas se realizó el test de lixiviado DIN 38414-S4, con el fin de valorar el riesgo y movilidad potencial de los diferentes analitos. En las muestras de lixiviado se midió el pH, CE, los iones mayoritarios y los metales Ni, Cu, Zn, As, Cd, Sb y Pb.

Los resultados han confirmado que la geodisponibilidad de los metales traza en la Sierra Minera está regulada por la meteorización fisicoquímica de los residuos minero-metalúrgicos, así como por la oxidación de los sulfuros metálicos asociados a los yacimientos de Pb-Zn.

Respecto a los mecanismo de transporte, dispersión y deposición de Ni, Cu, Zn, As, Cd y Pb, el balance de masas de metales traza geodisponibles en el Mar Menor reveló que la erosión eólica transfirió el 81 % de la entrada total de metales provenientes de la Sierra Minera, las aguas subterráneas contribuyeron en un 16 % y la escorrentía superficial en un 3 %. Todo ello demostró que la dispersión de estos contaminantes NO está controlada por las aguas continentales (escorrentía superficial y agua subterránea).

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1

Introduction

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There is a permanent exchange of chemical substances between the diverse forms of life and the environment in which they live. Geoenvironmental factors regulate such exchange and are crucial for health and welfare of all living beings on the planet. Figure 1.1 shows a flow chart where the different stages in the geochemical cycle of a trace metal are considered, from the natural abundances in the materials of the Earth crust, to the toxicity levels that affect an organism in particular. Some key concepts are described later, to better understand the geochemical cycle of the chemical elements, mainly the trace metals Ni, Cu, Zn, As, Cd, and Pb, which are the subject matter of this thesis.

Figure 1.1. Stages in the geochemical cycle of a trace metal, displayed between its natural abundance in the Earth crust and its toxicity in a recipient organism (modified from Smith and Huyck, 1999).

Trace-metal abundance Regional-local

Geoavailability:

Access and susceptibility to weathering

Physical dispersity Chemical mobility

Reception bodies:

Water-Soil-Air

Plants Animals

Degree of exposure

Residence time in the body:

Absorption-Excretion

Bioavailability

Toxicity

Less Trace-metal concentration More SourceTransportFate

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Trace metals play an important role in human health because some of them have abilities to support methabolic functions on the cellular level, deriving the maximum benefit in the right amounts. Others are only known to cause adverse effects. Anyway, toxicity of a susbstance is dose-dependent. Most of our knowledge about the biochemical reactions of metabolism involved with trace metals come from the twentieth century. However, evidence on the toxic health impact attributed to metals exposure dates back to the earliest civilisations. As an example, lead mining, metallurgy, and its popular use in cookware, drinking vessels, municipal water supplies, and baths are said to contribute to the decline of the Roman Empire. Similarly, chronic lead poisoning is a likely explanation for the dementia of many Roman emperors.

Rocks have the highest concentrations of metals. Their release to soil, water, and air is controlled by weathering processes. As a consequence, the natural occurrence of metals in soils and water is directly related to the distribution of the lithological types and their mineralogical composition. More than two thousands years ago, the Greek physician Hippocrates discovered relationships between diseases and geographic location, illustrating that environmental factors influence human health. Nowadays, there are geographical models that link diseases with the properties of soil, water, and aerosol particles. It has been difficult to prove cause-and-effect relationships between the overall metal concentrations and its toxic impact. Furthermore, the abundance of a particular metal in certain environmental scenery is not a good measure of its potential threat to human health. This is the reason why it is necessary to know its geoavailability.

1.1. TRACE-ELEMENT POLLUTION

Periodic table includes about 86 metallic elements and 7 metalloids, 73 of them can be considered as heavy metals, meaning that they have an atomic weight higher than Fe (55.85 g/mol). The concept of heavy-metal pollution would exclude polluting metals such as V, Mn, and Cr; and metalloids like As and Sb. It is more appropriate therefore to talk about trace-element pollution, although most of the inorganic pollutants are heavy metals.

Trace elements are present in the range 1–1000 mg/kg in the biosphere, being many of them required by living organisms, although may become toxic in case they surpass the permissible limits. However, contamination in soil sometimes comes from high levels of minor elements (e.g., Na, Fe, and Al). Table 1.1 shows a classification of the elements that play an important role in human diet.

In general, all trace elements are toxic when inhaled or ingested in sufficient quantities for a chronic-duration exposure. Moreover, elements such as Se, F, and Mo, have a short range of ppm of intake between which they behave in a healthy way.

Trace elements present in soils can be classified into five categories, based on their chemical behavior in soil solutions: (a) cations (e.g., Ag⁺, Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Zn²⁺), (b) uncombined elements (Hg, V), (c) oxyanions (AsO43–, CrO42–, MnO42–, HSeO3–, SeO42–), (d) halides (F^–, Cl^–, Br^–, I^–), and (e) metal-organic chelates

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(e.g., Ag, As, Hg, Se, Te, Tl chelates). Some of these elements may occur in more than one category.

Table 1.1. The role of chemical elements in the human body, in descending order of intake levels (Wikipedia, retrieved March 16, 2015, from https://en.wikipedia.org/wiki/Dietary_

element).

Elements Comments

O, C, H, N Organic basic elements

O, C, and H are major elements (10–100%) in the human body, and N is a minor element (0.1–10%).

S, K, Cl, Na, Ca, P, Mg Quantity elements

Require high daily dietary intake levels (4.7–0.4 g/day)^a All of them are minor elements in the human body, except for Mg, which is a trace element (1–1000 ppm).

Zn, Fe, Mn, Cu, I, Se, Mo, Co, Br, Ni

Essential trace elements

Require small daily dietary intake levels (<11 mg/day) Fe, Zn, Br, and Cu are trace elements in the human body.

The rest are in the nano-fraction range (1–1000 ppb).

Li, B, F, Si, V, Cr, As, Sr Possible structural or functional role in mammals

Require minimum daily dietary intake levels (<1 mg/day) F, Si, and Sr are present as trace elements in the human body. The rest are in the nano-fraction range.

aNo dietary intake defined for sulfur, as this element is obtained from proteins.

Table 1.2 lists the background ranges of some trace elements in the natural soils of the Region of Murcia, taken from Martínez-Sánchez and Pérez Sirvent (2007). They also reported generic referece levels for the same elements. These reference levels are the maximum acceptable concentrations for the human health and ecosystems, according to certain criteria. As reflected in this table, in the Sierra Minera, the usual Spolic Technosols in which mine and metallurgical wastes develop, can locally accumulate seriously abnormal concentrations of Zn, Cu, As, Cd, Sb, and Pb.

Seventeen trace elements have been identified in soils as very toxic because of their high degree of mobilization: Co, Ni, Cu, Zn, As, Se, Pd, Ag, Cd, Sn, Sb, Te, Pt, Hg, Tl, Pb, and Bi. Most of them are incorporated in the list of priority pollutants established by the US Environmental Protection Agency, which includes the following 13 trace elements: Be, Cr, Ni, Cu, Zn, As, Se, Ag, Cd, Sb, Hg, Tl, and Pb.

1.2. GEOAVAILABILITY

Geoavailability of a chemical element or compound in an earth material can be defined as the portion of it that can be liberated to the surficial or near-surface environment through mechanical, chemical, or biological processes (Smith and Huyck, 1999). Geoavailability of any substance is possible by the action of endogenous (internal geodynamics) and exogenous (external geodynamics) alteration processes.

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Table 1.2. Concentration ranges of some trace elements in soils of the Region of Murcia (Martínez-Sánchez and Pérez-Sirvent, 2007), compared to the abnormal values from the mine wastes of the Sierra Minera.

Element Background levels (ppm)

Generic reference levels (ppm)

Mine wastes levels (ppm)

Cr 24–45 38–71 25–80

Co 5–9 10–13 52

Ni 17–25 30–34 37

Zn 16–55 43–92 993–14720

Cu 12–23 23–32 18–268

As 5–8 8–12 1930

Se 0.2–0.6 0.4–0.5 n.d.

Cd 0.1–0.4 0.4–0.9 65

Sb 0.5–1.6 2–3 220

Hg 0.1–0.4 0.4–1.2 n.d.

Tl 0.1–0.4 0.5–0.8 n.d.

Pb 3–10 5–34 75–27780

n.d. not determined.

When a substance—polluting or not—is discharged in the environment, it does not remain permanently in the same place, being dispersed from this point, due to diverse physico-chemical and biological phenomena, which cause a transport inside the same environmental compartment, or between the different receiving environments, i.e.

atmosphere, hydrosphere, pedosphere, and biosphere.

1.3. MOBILITY

Mobility refers to the capacity of an element to move within fluids after dissolution.

It is difficult to be quantitatively predicted in surficial environments, because of the different behavior of elements under changing environmental situations. Some of the factors that control mobility include pH, solubility, sorption, and redox conditions.

Table 1.3 displays the relative mobility of chemical elements under different environmental circumstances (Smith, 2007).

1.4. SOLUBILITY

This term refers to the amount of a substance that can be dissolved in water at a given temperature and pressure. This parameter is used in environmental studies to help determine the fate of substances. Solubility in water is described by a solubility product (Ksp), which is the equilibrium constant for a solubility reaction. Some metals can make extremely insoluble compounds (very low Ksp values; e.g., Pb), so these metals tend to precipitate as solids and have limited mobility. Other metals (e.g., Zn) tend to be relatively mobile because they do not readily form insoluble solids. Due to the high sulfate concentrations in mining-influenced waters, metals that form strong bonds (and relatively insoluble precipitates) with sulfate would be expected to precipitate and be relatively immobile. However, metal complexation with these anions can increase dis-

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solved metal concentrations above what is usually observed for solubility reactions (Smith, 2007).

Table 1.3. Generalized relative mobility of chemical elements under different environmental circumstances (Smith, 2007).

Environmental conditions

Very mobile

Mobile Somewhat mobile Scarcely mobile to immobile

Oxidizing with

pH < 3 Br, Cd, Cl, Co, Cu, F, I, Ni, Rn, S, Zn

Al, As, Ca, Fe, Hg, K, Mg, Mn, Na, P, Ra, REE, Se, Si, Sr, U, V

Ag, Ba, Be, Bi, Cr, Cs, Ga, Ge, Li, Mo, Pb, Rb, Sb, Th, Ti, Tl, W

Sc, Sn, Y, Zr

Oxidizing with pH > 5 to

circumneutral, no iron substrates

Br, Cd, Cl, F, I, Rn, S, Zn

Ca, Mg, Mo, Na, Se, Sr, U, V

As, Ba, Bi, Co, Cr, Cs, Cu, Ge, Hg, K, Li, Mn, Ni, P, Ra, Rb, REE, Sb, Si, Tl

Ag, Al, Be, Fe, Ga, Sc, Sn, Th, Ti, W, Y, Zr

Oxidizing with pH > 5 to circumneutral, with abundant iron substrates

Br, Cl, F, I, Rn, S

Ca, Cd, Mg, Na, Sr, Zn

Ba, Bi, Co, Cs, Ge, Hg, K, Li, Mn, Ni, Rb, Sb, Se, Si, Tl

Ag, Al, As, Be, Cr, Cu, Fe, Ga, Mo, P, Pb, Ra, REE, Sc, Sn, Th, Ti, U, V, W, Y, Zr

Reducing with pH

> 5 to

circumneutral, no hydrogen sulfide

Br, Cl, F, I, Rn

Ca, Cd, Cu, Fe, Mg, Mn, Na, Ni, Pb, S, Sr, Zn

As, Ba, Co, Cr, Cs, Hg, K, Li, P, Ra, Rb, Si, Tl

Ag, Al, Be, Bi, Ga, Ge, Mo, REE, Sb, Sc, Se, Sn, Th, Ti, U, V, W, Y, Zr

Reducing with pH

> 5 to

circumneutral, with hydrogen sulfide

Br, Cl, F, I, Rn

Ca, Mg, Mn, Na, Sr

Ba, Cs, K, Li, P, Ra, Rb, Si, Tl

Ag, Al, As, Be, Bi, Cd, Co, Cr, Cu, Fe, Ga, Ge, Hg, Mo, Ni, Pb, REE, S, Sb, Sc, Se, Sn, Th, Ti, U, V, W, Y, Zn, Zr REE Rare-Earth Elements (which are treated here as a group, but individually can have somewhat different mobility behaviors).

1.5. METAL SPECIATION

Different chemical species of a given metal often have different mobility behavior and toxicological effects. Speciation is the distribution of an element amongst defined chemical species in a system. Distinct chemical species are chemical compounds that differ in isotopic composition, conformation, oxidation or electronic state, or in the nature of their complexed or covalently bound substituents.

The formation of metal complexes in solution tends to increase metal mobility.

Total metal concentration does not distinguish between the various species. For many metals, the free ion is thought to be the primary species that causes toxicity to aquatic organisms. Therefore, to achieve a reliable estimate of metal bioavailability, it is necessary to determine metal species. However, it should be noted that total metal

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concentration can provide an upper limit for estimation of metal bioavailability and toxicity (Smith, 2007).

Factors that can influence metal speciation include pH, redox conditions, inorganic ligands, organic ligands, and competition from other ions. Smith and Huyck (1999) provide a discussion of the links between metal abundance, mobility, bioavailability, and toxicity in mining environments.

1.6. EXPOSURE

It is defined as the contact between an agent and a target. Contact takes place at an exposure surface over an exposure period. Contact between a contaminant and an organism can occur through any route. The possible routes of exposure are: inhalation, if the contaminant is present in the air; ingestion, through food, drinking or hand-to- mouth behavior; and dermal absorption, if the contaminant can be absorbed through the skin.

Exposure to a contaminant occurs through multiple routes, simultaneously or at different times. In many cases the main route of exposure is not obvious and needs to be investigated carefully. For example, exposure to byproducts of water chlorination can obviously occur by drinking, but also through the skin, while swimming or washing, and even through inhalation from droplets aerosolized during a shower (Wikipedia, retrieved March 20, 2015, from https://en.wikipedia.org/wiki/Exposure_assessment).

Surface runoff and underground drainage in industrial, urban, and rural areas represent the main trace-metal input to water bodies accessible to human beings. In other cases, atmospherical pollution originates an occupational exposure by the inhalation of smoke and dust, where trace elements are in an uncombined state, or forming oxides, sulfides, and other combined forms. Exposure by dermal absorption is less frequent.

1.7. BIOAVAILABILITY

An element in a chemical state in particular is bioavailable if can be taken up by an organism and react with its metabolism. Regarding to plants, the bioavailable fraction includes the soluble and interchangeable forms in equilibrium with soil solution, which are controlled by different chemical reactions. In general, bioavailability is the degree in which a contaminant from certain source is free to move in or out an organism, depending on certain physiological and environmental factors.

Bioavailability of trace metals in soil is an efficient indicator of its quality, because its abundance has no link with the degree of uptake by plants. Bioavailability depends chiefly on the geochemical species in which the substance occurs. There is general agreement in the scientific community that metal chelation with EDTA and DTPA gives a right estimation of plants uptake from soil in standard conditions.

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1.8. TOXICITY

Toxicity is the degree to which a substance can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell (cytotoxicity) or an organ such as the liver (hepatotoxicity).

Paracelsus (1493–1541) stated that only the dose determined if a substance was poisonous or not. Toxicity is species-specific, making cross-species analysis problematic. Newer paradigms and metrics are evolving to bypass animal testing, while maintaining the concept of toxicity endpoints.

Clinical diseases or even death may appear in individuals exposed to high concentrations of non-essential elements. In most cases of acute exposure to toxic agents, the range and severity of the effects are directly related to dose. At lower doses, less severe side effects appear after a longer latency period.

Levels of certain trace metals, such as Ni, Cu, Zn, As, Cd, and Pb, are environmentally transcendent in preservation of soil, water, and biota. Their occurrence in the different reception bodies may have a geogenic (natural) or anthropogenic (human) origin. Open-pit metal exploitation at the global level, and the subsequent mineral processing techniques involved in the metal extraction (hydrometallurgy, pyrometallurgy, and electrometallurgy) generate a large amount of wastes which require a safe place for its storage and deposition. These areas should be physicochemically stable, to avoid the environmental risks associated to the presence of toxic metals and metalloids. A failure of the storage structures may facilitate the dispersion of these pollutants to the food chain. Trace-metal risk to human health and ecosystems is directly related to their solubility and bioavailability.

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2

Objectives and

Working hypotheses

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Heavy metals—and trace elements in general—are present in relatively low concentrations (1–1000 mg/kg) in the crust, soils, and plants. In addition, the presence of high heavy-metal concentrations—what can be considered as geochemical anomalies—often results in the formation of ore deposits. Mineral processing and metallurgical extraction of these deposits produce a high volume of solid wastes and mine waters which impact soils, waters, and ecosystems. A comprehensive study of heavy-metals geoavailability in mine areas is convenient to remedy this situation.

Degradation of soils by the accumulation of heavy metals is currently one of the urgent environmental challenges that society should approach. Characterization, evaluation, and remediation of polluted soils or water bodies are some of the major environmental demands to face within the framework of sustainable development.

Hazardousness of soil pollutants is determined not only by its total concentration but especially for the way they mobilise.

2.1. OVERALL AIM

The broad goal of this thesis is to contribute to the interpretation of the geogenic and anthropogenic factors, at local and regional levels, that control the geoavailability (solubility and mobility) of Ni, Cu, Zn, As, Cd, and Pb in the Sierra Minera de Cartagena – La Unión, as well as to assess the influence of the abandoned mining landscape on the Campo de Cartagena and Mar Menor lagoon.

In order to achieve this target, the thesis focuses on seven cathegories of specimens:

rainwater, surface runoff, groundwater, seawater, efflorescent sulfate salts, mining and metallurgical wastes, and parent materials. This study evaluates how those elements mobilise among the different environmental compartments.

2.2. PARTIAL AIMS

—To know the main rocks, wastes, and mineral phases enriched in the elements Ni, Cu, Zn, As, Cd, and Pb.

—To provide a spatial and temporal baseline set of data to characterise and understand how those metals mobilise under changing environmental conditions

—To establish a conceptual model for the geochemical cycles of those metals within the geological context

—To outline a geoavailable trace-metal mass balance for Mar Menor lagoon

—To evaluate the effectiveness of some remediation strategies over geoavailability and mobility of those metals in the Sierra Minera

—To propose preventive measures to reduce the geoavailability of those metals in the areas directly or indirectly affected by the abandoned mining activities

—To impact positively on future decisions about management of the mining area, providing a robust field data elucidation.

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2.3. WORKING HYPOTHESES

Reviewing the vast amount of information concerning the study area—and particularly the studies that integrate diverse field data, such as García (2004), Robles- Arenas et al. (2006), and Instituto Euromediterráneo del Agua (2009)—as a preliminary research hypothesis, it is postulated that geoavailability of trace metals in the Sierra Minera is controlled by physico-chemical weathering of mining and metallurgical wastes, as well as by the oxidation of metallic sulfides associated to the Pb-Zn ores. An additional assumption states that transport, dispersion, and deposition of Ni, Cu, Zn, As, Cd, and Pb are controlled by continental water bodies (surface runoff and groundwater).

In order to test both hypotheses, an in-depth examination of the hydrogeochemical cycles and the leaching potential—using the leaching test DIN 38414-S4—of those metals in the parent and waste materials were performed. The types and number of samples tested are described in Table 2.1.

Table 2.1. Summary of the working methodology planned for the current study. n.d. not determined.

Sample category Number of samples Sampling period Field trips Distance covered (km)

Rainwater 920 12/2004–3/2008 64 4966

Surface runoff 179 2/2005–12/2009 22 2195

Groundwater 127 11/2006–9/2009 35 2418

Seawater 16 4/2011–9/2012 2 205

Efflorescences 15 2/2005 1 n.d.

Types of mining and metallurgical wastes

7 5/2003–2/2005 1 n.d.

Lithological types 23 1/2012 1 n.d.

Total 1287 5/2003–9/2012 126 9784

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3

Literature review

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The Sierra Minera de Cartagena – La Unión has been the subject of intensive research by the scientific community since the early ‘60s of the 20^th century up to the present day. The first studies focused on the description of the geological setting, trying to establish a conceptual model of the different mineral deposits found in the area.

Nowadays, researcher’s efforts and challenges have to do with a detailed description of the environmental implications that an abandoned mining landscape arises. Although multiple references are spread all over the chapters and papers that cover this thesis, a sampling of the core topics scrutinized in the area are collected below.

3.1. GEOLOGICAL SETTING

A comprehensive overview of the different types of ore deposits found in the Sierra Minera can be found in:

 Pavillon (1969), who explained that the three volcanic episodes redistributed upwardly the pre-existing mineralizations, forming ore bodies called pyritic manto and manto of silicates. Miocene mineralizations were added later on the previous ore bodies.

 Oén et al. (1975) described the three facial types of parageneses found in the Pb- Zn-Fe ores of La Unión. They distinguished a central, an intermediate, and an outward zone, with different mineralizations. They also proposed a lithologic succession and a provisional tectonostratigraphic division for the ore district.

 Ovejero et al. (1976) recognized four superimposed tectonic units, covered by a Miocene distorted layer. They proposed one lithostratigraphic column for each tectonic unit.

 Manteca and Ovejero (1992) took into account previous work undertaken in this field, describing the tipology of the mineralized bodies. They also estimated the magnitude of the ore bodies mined in the 20^th century, compared to the original amount of mineral deposits.

 The most recent revisions of the conceptual framework related to the different ore bodies found in the area were conducted by Pujol et al. (2013), Sanmartí et al. (2013), and Soler et al. (2013), who labelled those mineralization as Pb-Zn- Ag-(Sn).

3.2. MINING HERITAGE

Some studies involving the importance of a heritage policy to protect and recover the material remains that have been kept throughout the centuries are:

 Manteca et al. (2008), where the authors were deeply concerned about the situation of abandonment and deterioration of the ancient and modern heritage in the nining district of Cartagena – La Unión.

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 Castejón et al. (2014) dealt with the recent adaptation of Agrupa Vicenta mine to be visited as a museum. According to the authors, the tourist exploitation of this underground mine has accelerated the weathering processes inside, diminishing the structural stability of the enclosing rocks.

3.3. GEOPHYSICS AND GEOTECHNICAL ENGINEERING

Geophysical techniques are powerful tools to improve the understanding of the properties of mine wastes in the Sierra Minera. Examples of these studies include:

 Martínez-Pagán et al. (2009), who used electrical resistivity imaging combined with soil chemical analysis to determine the structural characteristics of mine tailings ponds, in order to assess efficient measures of environmental protection.

 Rodríguez et al. (2011) studied parameters of geotechnical interest in tailings dams, such as plasticity index, permeability, internal friction angle, cohesion, and other variables, concluding that high water saturation is the leading cause to dams failure.

3.4. MINING AND METALLURGICAL WASTES

A lot of researchers gathered information about the impact of mining and metallurgical wastes on the environment, from different perspectives:

 García (2004) and Robles-Arenas et al. (2006) made innovative efforts to integrate multiple field data to assess the true environmental impact and potential risk of this abandoned sulphide-mining site.

 Navarro et al. (2008) studied tailings and soils near Cabezo Rajao mine, evaluating the dispersion of soluble and particulate materials towards the surroundings of Mar Menor lagoon. They also showed the stabilization role of carbonate minerals in soils, to limit the geoavailability of the contaminants studied.

3.5. SOIL AND SEDIMENT POLLUTION

Sedimentation plains of wadis and the surrounding soils have been particularly affected by mining activities, provided that until 1956, post-flotation wastes were allowed to be discharged directly on the wadi beds. Some of the studies that deal with this issue are:

 González-Fernández et al. (2011), who investigated the distribution and mobility of some trace elements in the alluvial plane of El Beal wadi. Chemical profiles of soils, in-depth sediments, and plant species were carried out by using X-ray techniques. Mobility was assessed by lixiviation test runs.

 Zornoza et al. (2012) identified trace-metal contamination along Avenque (Gorguel) wadi, by characterizing the downstream distribution of metals in the

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stream sediments, the chemical profile of surface water, and the metal accumulation in the stream vegetation.

3.6. POLLUTION OF CONTINENTAL WATERS

Surface runoff and groundwater reservoirs are largely affected by acid mine drainage, altering its chemical composition and having toxic effects on ecosystems. A picture of the subject appears on:

 Robles-Arenas and Candela (2010), who characterized the regime and quality of the groundwater system after the mine closure. A marked sulfate concentration, acidic pH, and high heavy-metal loads reflected the magnitude of the problem.

 CHS (2015), the hydrographical authority of the Segura river basin (Confederación Hidrográfica del Segura) have been conducting hydrogeological monitoring studies on groundwater, surface water, springwater, and wetlands.

Some of the reports produced in the period 2006–2014 included sampling points in the area affected by mining activities.

3.7. MAR MENOR AND SURROUNDING PROTECTED LANDSCAPES Mar Menor lagoon is included on the Ramsar Convention list for the conservation and sustainable utilization of wetlands. The impact of mine wastes on this shallow body of water—and surroundings—is mentioned in several papers:

 Marín-Guirao et al. (2007) studied the pulse entrance of mining wastes through two temporary streams into the Mar Menor coastal lagoon in two torrential rain events. They stated that the particulate metals affected a wider area than the dissolved heavy metals. Both types of pollutants are finally accumulated in the sediments of the lagoon.

 Instituto Euromediterráneo del Agua (2009) is a collection of papers that provide an overview of the current scientific knowledge concerning the Mar Menor lagoon, under different perspectives, disciplines, and methodologies.

 Conesa et al. (2014) studied the phytomanagement of Marina del Carmolí, a salt marsh polluted by mining wastes, concluding that spontaneous vegetation is a good option to improve the ecological indicators and to prevent the transport of pollutants to nearby areas.

3.8. ENVIRONMENTAL REMEDIATION AND ECOLOGICAL RESTORATION

Once assessed the contamination on a particular site, several authors studied how to immobilize the pollutants, evaluating the feasibility of restoration strategies:

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 Zanuzzi and Cano (2010) recognized that revegetation is a very difficult task in the Sierra Minera, due to the physicochemical properties of the soils and the aridity of the climate. The aim of the work was to achieve the chemical inmobilization and phytostabilization of Pb-polluted soil in an acidic mining pond. After two years of adding organic and lime amendments, a reduction in Pb mobility and plant colonization were both observed, showing that the method was a successful alternative of reclaiming this mining area.

 Gómez-Ros et al. (2013) described the first ecological restoration of a tailings area in La Unión mining district. After 30 years since the wastes were ‘sealed’

with a 0.5-m layer of soil, the bottom-up flux of heavy metals persisted, what revealed a high metal mobility and the inefficacy of the restoration procedure.

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4

Characterization

of the study area

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An analysis of the different variables affecting the environment of the study area is carried out in this chapter. Mining and metallurgical operations have been focused on the central belt of the Sierra de Cartagena – La Unión (also called Sierra Minera in a simplified manner), where significant mineralization is found (Figure 4.1).

4.1. Geographical location and landscape relief

The Sierra Minera comprises a coastal mountain range with an approximate E–W trend, located in the SE of the Region of Murcia (Spain). It is limited by the Mediterranean Sea to the South and the East, and by the Campo de Cartagena plain to the North. It extends over an approximate area of 100 km², with a length of 23 km and a width of 4 km. Sierra Minera is included in the municipalities of Cartagena and La Unión, and the main municipal districts, in an East–West direction, are Cabo de Palos, Los Belones, Campo de Golf, El Estrecho de San Ginés, Llano del Beal, Portmán, La Unión, Alumbres, Escombreras, Vista Alegre, and Cartagena.

Figure 4.1. Geological map of Sierra de Cartagena – La Unión (Robles-Arenas et al., 2006).

The central belt of the Sierra Minera covers an area of roughly 50 km², straddling part of Cartagena and the entire La Unión municipalities. To the west, it has borders with La Parreta (Alumbres), El Machón, and Pico del Horcado mountains, towards Cabezo del Aljibe and El Gorguel Bay. It is bounded to the east by Los Blancos mining area, Atamaría spot, and Portman Bay.

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The highest elevation is the triangulation station Sancti Spiritus 3 [396 mamsl (meters above mean sea level)], located in the middle of the area affected by mining activities. In an East–West direction, other important summits are Cabezo de la Fuente (336 mamsl) in the south of Los Belones, Monte de las Cenizas (307 mamsl) southeast of Portman, Peña del Águila (389 mamsl) northwest of Portman, Sierra de la Fausilla (364 mamsl) in the south of Escombreras Valley, Sierra Gorda (306 mamsl) in the North of Escombreras Valley, and Cabezo de San Julián (294 mamsl) southeast of Cartagena.

The northern slopes are gentler than southern ones (Figure 4.2). The latter end as cliffs on the coast of the Mediterranean Sea, with slopes greater than 15%. There are several coves, some of them accessible only by sea, such as Huncos, Mulas, Cuervo, and Golera; others are also accessible by land, like Reona, Calblanque, Portman Bay, and Gorguel. There are three main headlands: Cabo de Palos, Cabo Negrete (by the Monte de las Cenizas), and Cabo de Agua (by the Sierra de la Fausilla).

Figure 4.2. Slope map (modified from ITGE, 1999).

4.2. Surface water and groundwater hydrology in the Sierra Minera

The hydrographical network mainly consists of ten wadis, only operational during heavy rainfall events. Five of them flow into the Mediterranean Sea (Carrasquilla, Ponce, Beal, Matildes, and Miedo) and the remaining into the Mar Menor lagoon (Portmán, Gorguel, Escombreras, Santa Lucía, and Hondón), with the longest being 11.6 km (Miedo, northern face) and the shortest 2.8 km (Portmán, southern face)

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(Figure 5.7 and Table 5.2). In the northern face, the wadi beds disappear before arriving to the Mar Menor lagoon, except when they are forced into artificial channels.

From a hydrogeological point of view, the Sierra de Cartagena – La Unión aquifer behaves as a single hard-rock aquifer, outcropping over an area of approximately 100 km². This aquifer underlies the Campo de Cartagena basin and the Mediterranean Sea, being difficult to define its boundaries with accuracy. The aquifer is composed of geologic materials of the Internal Zones of Betic Cordillera, mainly schists, quartzites, phyllites, limestones and marbles, and ranging 400–800 m of thickness. The impervious basement is the lower Nevado-Filábride (N-F) unit (schist and quartzite). It shows secondary porosity due to the intensive tectonic activity, mining activities and, to a lesser extent by karstification. The aquifer recharge exclusively originates from rainwater infiltration; according to Confederación Hidrográfica del Segura (CHS), 30%

of rainwater is infiltrated and an estimated 15% accounts for runoff. The discharge.is produced by intense evaporation from large diameter wells and open-pit lakes (Brunita, Gloria, and Los Blancos II). Moreover, on the northern slope two springs exit (El Chorrillo and La Fuente) and a seepage from a mining gallery (Horno 33 road). On the southern side, there is discharge through four mining galleries (Portmán gallery, Lilian tunnel, José Maestre tunnel, and Molienda semiautógena) and two springs (Gorguel and Barranco del Moro). Also, water is extracted from water-supply wells for the existing industries and golf-field irrigation; however, extraction volumes are not known with accuracy. According to 1993 data (IGME-MOPTMA, 1996), 1.4 hm³ were pumped.

Water flow to the Campo de Cartagena hydrogeologic unit and to the Mediterranean Sea must exist. Discharge to the Mediterranean Sea is estimated to be 0.3 hm³/y by CHS. Flow to the Campo de Cartagena remains unknown (Robles-Arenas et al., 2006).

4.3. Climatology

The climate in the Sierra de Cartagena – La Unión is typical of a dry-summer sub- tropical Mediterranean region, characterised by an annual precipitation ranging 250–350 mm, irregularly distributed in a few intensive rainfall events. The southern face is wetter than the northern one, due to the air-moisture condensation from the Mediterranean Sea.

The area exhibits a temperature between 5 (January) and 40 ºC (August). The annual average temperature is 17 ºC.

Wind is always present in the study area. Levante wind (in the western Mediterranean coastal area this is the wet wind coming from the eastern direction, that of the rising Sun) is dominant in dry seasons, whereas Poniente (wind that blows from the West) is more common in wet seasons. The lowest average wind speed is registered in autumn (16 km/h) and the fastest in spring (22 km/h). Estimates of annual evapotranspiration (ETp) range from 800 to 1200 mm/y, depending on the estimation method (Robles-Arenas et al., 2006).

4.4. Soils and vegetation

Due to the climate, soil development is scarce. Usual soil types are Haplic and Petric Calcisols, Calcaric and Haplic Cambisols, Gipsiric and Calcaric Regosols, and

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some types of Leptosols. In many areas, these types have been replaced by Terric and Hortic Anthrosols, Spolic Anthric Regosols, etc. (Robles-Arenas et al., 2006).

Vegetation is mainly composed by shrubs, although small areas are being reforested by Pinus halepensis. A lot of endemisms and iberoafricanisms have been reported, growing some native plants occasionally on tailing dams.

Study area is located in the domain of the Thermomediterranean Murcian-Almerian Series of cornical (Periploca Angustifolia). This plant community extends parallel to the coast from Cabo de Palos to Cartagena and beyond. Apart from this thorny shrub, other species present include esparraguera (Asparagus horridus), black hawthorn (Rhamnus lycioides), arto (Maytenus senegalensis), European fan palm (Chamaerops humilis), acebuche (Olea europaea, ssp. sylvestris), carob tree (Ceratonia siliqua), arar (Tetraclinis articulata), aliaga (Calicotome intermedia), mastic (Pistacia lentiscus), Aleppo pine (Pinus halepensis) and esparto (Stipa tenacissima) (Figure 4.3). The distribution of the different species varies depending on the available moisture of the soil, outcropping of limestone rocks, influence of sea wind, and altitude (García, 2004).

Plant associations characteristic of the mature stages in this landscape comprise (Figure 4.4):

 Arto (Maytenus senegalensis, ssp. europaea) – cornical (Periploca Angustifolia). Association extended along the coasts of Murcia and Almería, a frost-free area with an average temperature higher than 17 ºC. It is a xerophytic vegetation adapted to survive with little or no rain, but taking advantage of the atmospheric humidity provided by its proximity to the sea, which reduces evapotranspiration and increases water availability. This ecological community combines thorny scrubland (cornical, arto, European palm fan, esparraguera, and black hawthorn) with acebuche and carob tree, where anthropic degradation of landscape by mining activities makes it possible.

 European fan palm (Chamaerops humilis) – black hawthorn (Rhamnus lycioides). This plant community is found close to the previous association, in areas with higher continental features, where mild night frosts are possible—

northern slope in the high mountain locations.

 Flor de la estrella (Lapiedra martinezii) – esparto (Stipa tenacissima). This association forms esparto fields that lie over medium-depth soils of different types. Esparto is accompanied by some small Poaceae [such as dactilo (Dactylis glomerata ssp. Hispanica), Avenula murcica, and Helictotrichion Filifolium] and geophytes [such as Distichoselinum tenuifolium, Flor de la estrella (Lapiedra martinezii), and round-headed leek (Allium sphaerocephalon)]. This plant community is the first degradation stage of high scrubland, forming dense areas in sunny spot hillsides.

 Manzanilla yesquera (Phagnalon saxatile) – Euphorbia squamigera.

Association located on stony soils, at the foot of ledges, and in sunny spot hillsides. They form a set of nitrophilous species characteristic of the Meso and Thermo-Mediterranean habitats.

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Figure 4.3. Different plant species native to Sierra Minera: (a) Cornical (Periploca Angustifolia), (b) Esparraguera (Asparagus horridus), (c) Black hawthorn (Rhamnus lycioides), (d) Arto (Maytenus senegalensis), (e) European fan palm (Chamaerops humilis), (f) Acebuche (Olea europaea, ssp. sylvestris), (g) Carob tree (Ceratonia siliqua), (h) Arar (Tetraclinis articulata), (i) Aliaga (Calicotome intermedia), (j) Mastic (Pistacia lentiscus), (k) Aleppo pine (Pinus halepensis), and (l) Esparto (Stipa tenacissima).

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Figure 4.4. Some plant associations characteristic of the Sierra Minera, from left to right:

(a) Arto (Maytenus senegalensis, ssp. europaea) – cornical (Periploca Angustifolia), (b) European fan palm (Chamaerops humilis) – black hawthorn (Rhamnus lycioides), (c) Flor de la estrella (Lapiedra martinezii) – esparto (Stipa tenacissima), (d) Manzanilla yesquera (Phagnalon saxatile) – Euphorbia squamigera.

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4.5. Geologic setting

Sierra de Cartagena – La Unión belongs to the Internal Zones of the Betic Cordillera. The Betic and Rift cordilleras, lying from north to south of the Alborán Sea, form an arc-shaped mountain belt joining across the Strait of Gibraltar. They were

developed during the convergence between the African and Iberian plates (late Mesozoic to Cenozoic). The Internal Zones comprise three complex nappes of variable metamorphic grade, which are from bottom to top: the Nevado-Filábride (N-F), the Alpujárride (Alp), and the Maláguide complex (MC) (Figure 4.5). The grade of metamorphism decreases in each complex from bottom to top, and from the lower complex to the upper. The N-

Figure 4.5. Simplified litho-structural column of Sierra de Cartagena – La Unión central zone (Manteca and Ovejero, 1992).

F is divided into two parts: the lower is constituted by graphite micaschists, greyish quartzites, and quartzitic schists, locally named el muro (the wall), with a minimum thickness of 500 m, from the Paleozoic era or older. The upper N-F consists of micaschists, white quartzites, marbles and green rocks. It has a thickness of 60 m approximately and belongs to the Permo-Triassic age. Green rocks are massive bodies of ortho-amphibolites with chloritic schists. Discordantly overlaying the N-F is the Alp complex, which is constituted from bottom to top by San Ginés unit, Portman unit and Gorguel unit. All units present a detritic formation (epimetamorphics rocks, quartzites and phyllites), probably of Permian age, and a Triassic carbonate series. Intrusive bodies of diabases and dolerites in the carbonated material of San Ginés unit are present. Their thicknesses are approximately 30 m to Gorguel unit, 150 m to Portman unit, and 250 m to San Ginés unit, where they are well developed. MC has a detritic component (sandstone, quartzite, silt and conglomerate) and a carbonated member (limestone).

The tectonic complexes are partly covered by Miocene and Quaternary sediments (pelitic rocks, including sandy and conglomeratic levels) and affected by subvolcanic (rhyolite–dacite and andesite) and volcanic events (alcalin basalt). These Tertiary formations are modified by tectonic movements. Posterior to the complexes being piled up, between the Eocene and Middle Miocene period, an extensional phase generated two important fault systems, N-70 and N-130 (Figure 4.6), which control the magmatic outcrops. Sierra de Cartagena – La Unión presents geological horst and graben features as a consequence of the reactivation of these faulting systems after the Middle Miocene.

N-70 faults represent the trend of a great volcanic axis cut by a set of second-order horst and graben structures trending N-130.

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4.6. Mineral deposits

The main mineralisation is constituted by two stratabound sulphide deposits, locally named mantos, on the carbonated sequences in the N-F (second manto) and Alp complex (first manto) (Figure 4.5). The mineralization can also be found disseminated in Miocenic materials, in gossans, stockworks and veins. The Pb–Zn and

Figure 4.6. Schematic block diagram of Sierra de Cartagena – La Unión (Gagny and Marconnet, 1994).

associated ore deposits are described by Oén et al. (1975). Two mineral parageneses appear in both stratabounds.

The first is a chlorite–sulphide–carbonate–silica paragenesis, named manto piritoso, where sulphide minerals are pyrite, sphalerite, marcasite, galena, and locally pyrrhotite, being chalcopyrite, arsenopyrite, tetrahedrite and stannite accessory constituents;

carbonate minerals are siderite with Zn- and Mn-bearing varieties, and rarely calcite.

Silica occurs as quartz. Clay minerals and chlorite are frequent.

The second paragenesis is greenalite–magnetite–sulphide–carbonate–silica, named manto de silicatos o de magnetita, where sulphide and carbonate minerals are the same of previous paragenesis. Greenalite is highly abundant, locally accompanied by chlorite, clay minerals, talc or minnesotaite. Magnetite is also plentiful, however rarely does it show oxidation in hematite. Silica occurs as quartz, opal, chert and veins of chalcedony.

Miocenic disseminations consist of pyrite, marcasite, galena, and are mixed with chlorite and quartz; accessory minerals are pyrrhotite and chalcopyrite. In gossan zones, ores occur as an oxide–hydroxide–sulphate–carbonate–silica association; iron oxides are goethite, hematite, and magnetite, being manganese oxides also present. Among the sulphates are barite, anglesite, jarosite, alunite, anhydrite and gypsum; carbonates are calcite, siderite, cerussite and smithsonite; silica appears as quartz, chert, calcedony and opal; and finally, clay minerals (vermiculite, meta-halloysite, and dickite) are locally abundant.

There is a controversy with regard to the genesis of the mineralisation; there are two hypotheses. The first hypothesis establishes a mineralisation generated by hydrothermal activity related to Tertiary volcanism. The second hypothesis considers two metallogenetic phases, the main phase being pre-orogenic, and the second one associated with the Neogene volcanism (Robles-Arenas et al., 2006).