Geochemical Anomalies of Critical Elements (Be, Co, Hf, Sb, Sc, Ta, V, W, Y and REE) in Soils of Western Andalusia (Spain)

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ “This is an Accepted Manuscript of an article published by Elsevier in: APPLIED CLAY SCIENCE on 2020, available at: https://doi.org/10.1016/j.clay.2020.105610” 1 Geochemical anomalies of critical elements (Be, Co, Hf, Sb, Sc, Ta, V, 1 W, Y and REE) in soils of western Andalusia (Spain) 2 Juan Carlos Fernández-Caliania, Antonio Romerob; Isabel Gonzálezb; Emilio Galánb 3 a Department of Earth Sciences, Faculty of Experimental Sciences, University of 4 Huelva, Campus de El Carmen, 21071 Huelva, Spain 5 6 b Department of Crystallography, Mineralogy and Agricultural Chemistry, Faculty of 7 Chemistry, University of Seville, Campus de Reina Mercedes, 41071 Seville, Spain 8 9 10 Abstract 11 12 A collection of 694 soil samples was taken from 367 sites (at a density of 1 site 13 per 120 km2) in the western of Andalusia (SW Spain) to establish regional geochemical 14 background of emerging critical elements on the <2 mm soil fraction, and provide 15 threshold values for anomaly detection to support mineral exploration in the survey 16 area. The spatial distribution pattern of the soil geochemical anomalies is primarily 17 influenced by the occurrence of magmatic alignments and metallogenic belts in the 18 southern zones of the Iberian Massif. Soils over granitic parent materials are marked by 19 W, Be, Ta and REE anomalies, whereas those derived from mafic igneous rocks contain 20 anomalous concentrations of Sc, Co and V. Most of the threshold exceedances for Hf 21 and Sb appear to be linked to soils on pelitic metasediments. The distribution of Sb and 22 Co outliers is also related to sulfide ore occurrences in the bedrock and could be 23 affected by anthropogenic influences. The Santa Olalla igneous complex, the 24 granodioritic pluton of the Los Pedroches batholith and the magmatic alignment of 25 Villaviciosa de Córdoba-La Coronada may represent exploration opportunities for high-26 tech elements, mainly for REE, although the identification of promising areas requires 27 further investigation. 28 2 29 keywords: High-tech metals, geochemical baseline, threshold values, anomaly 30 detection, soil exploration geochemistry. 31 32 1. Introduction 33 34 There are growing concerns about the long-term security of supplies of raw 35 materials that are crucial to modern technology and society. Variously referred to as 36 critical, strategic or high-tech metals and metalloids, these elements are currently 37 produced in small quantities as by-products, they are increasingly used in a range of 38 high-technology and clean energy applications, and have no effective substitutes 39 (Graedel et al., 2015). The risks of supply shortage and their impacts on the global 40 economy are higher compared with most of the other raw materials, due to the fact that 41 a high share of the worldwide production is only concentrated in a few countries, with 42 China being the leading supplier. 43 44 Criticality is a subjective and dynamic concept. Each country or groups of 45 countries develop their own lists of critical elements and minerals based on their 46 industrial and strategic interests (Hayes and McCullough, 2018). Criticality assessments 47 are subject to change with time and hence that lists are subject to regular update and 48 revision. In Septembre 2017, the European Commission (EU) issued an updated list of 49 critical raw materials with a high supply-risk and a high economic importance for the 50 European Union (European Commission, 2017), which is used to incentivise the 51 production of strategic minerals and metals and facilitate the launching of new mining 52 and recycling activities. Some elements listed by the EC include: Be, Bi, Co, Ga, Ge, 53 3 Hf, In, Mg, Nb, P, Sb, Sc, Ta, V, W, Y, platinum-group metals (PGM) and rare earth 54 elements (REE). They are increasingly used in the manufacture of mobile phones and 55 computers, LCD screens, electric cars, solar panels, rechargeable batteries, medical 56 devices and many other high-tech applications and products. All these elements are 57 located within the criticality zone (supply risk ≥ 1 and economic importance ≥ 2.8) of 58 Figure 1. 59 60 Most of the critical elements are typically found in low concentrations in 61 primary ore deposits of major metals but they are cycled during chemical weathering, 62 pedogenesis and other surface processes, hence soil and regolith developed on 63 mineralized bedrock areas can be enriched in such elements (Jowit et al., 2017, Négrel 64 et al., 2019). Thus, for instance, clay deposits and clayey soils containing high 65 concentrations of exchangeable REE that are thought to be adsorbed on clay minerals, 66 dominantly kaolinite and halloysite, have become a critical mineral resource in China 67 (Bao and Zhao, 2008). Therefore, the identification of significant geochemical 68 anomalies in soils and weathering crusts is a key issue in mineral exploration of high-69 tech elements. 70 71 Andalusia is a region in the South of Spain with a long history of mineral 72 exploration and mining, particularly for pyrite and iron oxides, and it is currently a 73 major contributor to world supply of base metals, notably Cu, Pb and Zn. However, the 74 potential for trace elements that are regarded as critical has not been assessed. 75 Andalusia’s geology is relatively well endowed with a wide variety of mineral deposit 76 styles and thought to be prospective for a range of commodities (García-Cortés et al., 77 2011). Its potential for discovering new deposits of strategic metals and metalloids in 78 4 soil and regolith profiles remains high, but the occurrence, extent and grade of these 79 non-conventional deposits are not well known or not published. 80 81 This paper was intended to improve the knowledge base of critical raw materials 82 resources and their potential in western Andalusia, highlighting areas for future research 83 in geochemical prospecting. The main objectives were: 1) to define the soil geochemical 84 baseline of selected critical elements; 2) to provide threshold values for anomaly 85 detection; and 3) to explain the source and factors influencing the distribution of the 86 major soil geochemical anomalies. 87 88 2. Regional bedrock geology 89 90 The survey area encompasses about 45,400 km2 of the western provinces of 91 Andalusia, namely Huelva, Sevilla, Cádiz and Córdoba, covering a large part of 92 southwestern Spain (Fig. 2). The most common soils across the study area are 93 Cambisols, Leptosols and Regosols (WRB, 2014). The geology of the area can be 94 delineated into three major zones representing distinct geotectonic environments: 1) the 95 Iberian Massif, widely exposed across the north, consisting mainly of Palaeozoic 96 sedimentary formations that were metamorphosed and deformed during the Variscan 97 orogeny and intruded by granitoids; 2) the Betic Cordillera to the south where the 98 geology is dominated by Mesozoic and Cenozoic sediments deformed by the Alpine 99 tectonics; and 3) the Guadalquivir Basin, an elongated foreland basin developed during 100 the Neogene and Quaternary between the Iberian Massif and the Betic Cordillera. 101 102 5 The basement terranes outcropping in the study area correspond to three 103 tectonostratigraphic zones of the Iberian Massif (Julivert et al., 1972): Central-Iberian 104 Zone, Ossa-Morena Zone and South-Portuguese Zone, which are the westernmost 105 exposures of the European Variscan Belt. On the other hand, the outcropping rocks of 106 the Betic Cordillera belong to the Subbetic Domain of the External Zone and the flysch 107 units of the Campo de Gibraltar Complex. A comprehensive review of the regional 108 geological setting can be found in Gibbons and Moreno (2002) and Vera (2004). Here 109 are summarized the main lithologic features and the metallogenic framework of the 110 bedrock areas. 111 112 The Central-Iberian Zone (CIZ) is characterized by the occurrence of a long 113 elongated magmatic body known as Los Pedroches batholith (e.g. Donaire et al., 1999), 114 consisting of a granodiorite pluton, a dyke swarm and a suite of monzogranite plutons 115 that intruded into low-grade metamorphic rocks of Late Precambrian to Carboniferous 116 ages. The host rocks belong to an Early Carboniferous sequence composed of 117 alternating slates and greywackes (facies Culm). To the north of the batholith, the 118 Precambrian basement is formed by a thick succession of schists and greywackes, while 119 to the south there is a series of black schists and metagreywackes with intercalations of 120 amphibolites and volcanic-sedimentary rocks. These are, in turn, unconformably 121 overlain by Cambrian carbonatic and siliciclastic sediments. The batholith encloses 122 many hydrothermal vein-type deposits that have been mined in ancient times for a 123 variety of valuable metals like Cu, Pb, Zn, Ag, Sn, W, Sb, Co and Bi (Locutura et al., 124 1990). 125 126 6 The Pre-Ordovician rocks of the Ossa-Morena Zone (OMZ) are similar to those 127 described for the south CIZ of the Los Pedroches batholith. The Ordovician-Silurian-128 Devonian sucessions consist mainly of slates, sandstones, black shales and quartzites, 129 while the Upper Devonian-Carboniferous syn-orogenic sediments are dominated by 130 turbidites with minor volcanic and conglomeratic intercalations. The complex 131 geological evolution of the OMZ has produced a wide range of mineralization styles 132 (Tornos et al. 2004), including volcanic-hosted massive sulfides (VHMS), sedimentary-133 exhalative deposits, skarns and replacements, orthomagmatic ore bodies, and a variety 134 of metal-bearing hydrothermal veins. 135 136 The South-Portuguese Zone (SPZ) is the southernmost tectonic segment of the 137 Iberian Massif. The most remarkable feature of the SPZ is the occurrence of several 138 VHMS deposits of world-class importance forming the Iberian Pyrite Belt (IPB). The 139 oldest rocks exposed within the IPB form a terrigenous sedimentary sequence composed 140 of phyllites and quartzites with some limestone lenses at its top of Upper Devonian age, 141 which is overlain by bimodal volcanic rocks within a sedimentary framework. This 142 volcanic-sedimentary complex is covered by turbiditic sediments (flysch deposits) with 143 an Early Carboniferous age, and it is the host for the VHMS deposits and numerous 144 manganese occurrences. About 60 mines have operated during the last century mainly 145 for pyrite, although most orebodies contain appreciable amounts of Cu, Pb and Zn, 146 precious metals and a wide variety of trace elements, such as As, Bi, Cd, Co, Hg, Sn, 147 and Se (e.g. Leistel et al., 1998; Tornos, 2006). 148 149 The External Zone of the Betic Cordillera corresponds to the Mesozoic and 150 Tertiary sedimentary cover of the Iberian Massif. The Subbetic domain of the External 151 7 Zone forms a complex of thrust nappes comprising Triassic to Middle Miocene 152 sedimentary successions with local volcanic and subvolcanic mafic rocks. In general, 153 the Triassic terrains are composed of red detrital sediments and evaporites, the Jurassic 154 is represented by marine carbonate deposits (dolostones and limestones), and the 155 Cretaceous is characterized by a predominance marly limestones. The flysch units of the 156 Campo de Gibraltar Complex (CGC) contain a series of tectonic units, mainly turbiditic, 157 and olithostrosmal formations which range from Cretaceous to Early Miocene. 158 159 Finally, the Neogene infill of the Guadalquivir Basin comprises five offlapping 160 depositional sequences that are progressively younger to the west (Sierro et al., 1996). 161 The basin is filled with autochthonous sediments (calcarenites, bioclastic limestones, 162 clays, silts and sands) that unconformably overlie the Iberian Massif, and allochthonous 163 units consisting of gravity-flow deposits (olistostromes) linked to the southern active 164 margin, as a result of the dismantling and erosion of the overthrusted nappes from the 165 Betic Cordillera. 166 167 3. Soil sampling and methods 168 169 A total of 694 soil samples were collected from 367 sites unevenly distributed 170 over the study area, with a sampling density of about one site per 120 km2. In an attempt 171 to reduce selection bias, the sample locations were chosen using a stratified random 172 sampling strategy based on bedrock geology, as lithology of the parent materials is the 173 main soil-forming factor controlling the soil geochemistry in the area (e.g. Galán et al., 174 2008). The sites were chosen to represent rural areas with no direct source of pollution 175 other than atmospheric deposition and diffuse contamination from human activities. 176 8 Sampling was avoided in agricultural ecosystems to prevent contamination from 177 fertilizers. 178 179 Soil core samples were taken with an Edelman auger from a depth of 0-20 cm 180 (367 topsoil samples) at all sites, and from a depth of 20-40 cm (327 subsoil samples) in 181 those locations where the bedrock was encountered at greater depths below the ground 182 surface. In order to improve statistical confidence, the samples were bulked in the field 183 to make a composite sample of about 4 kg per depth interval, at each site, from five soil 184 cores collected in crossing directions and spaced approximately 1.5 m around the 185 central sampling position. The soil samples were dried at ambient air temperature, 186 gently disaggregated with a wooden roller, sieved to pass a 2-mm stainless steel screen 187 and then thoroughly mixed to ensure homogeneity. A subsample of each sieved soil was 188 ground using an agate mortar to recover the less than 63 µm grain-size powder for 189 chemical analysis. 190 191 The samples were analyzed for Be, Co, Hf, Sb, Sc, Ta, V, W, Y and some REE 192 (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) at Activation Laboratories Ltd. (Ontario, Canada), 193 which is accredited to the ISO/IEC 17025 Quality System. For all the elements, except 194 Be, V and Y, total concentrations were determined by instrumental neutron activation 195 analysis (INAA). A 30 g sample was irradiated at a thermal flux of 7 x 1012 neutrons 196 cm-2 s-1. After a seven-day decay period, the samples were counted on a high resolution 197 Ge detector. The decay-corrected activities were compared to a calibration obtained by 198 using multiple certified international reference materials. From 10-30% of the samples 199 were rechecked by re-measurement and one standard was run for every 11 samples. 200 Yttrium, V and Be determinations were conducted by inductively coupled plasma-201 15 distribution patterns of these metals are rather similar, as they appear strongly correlated 352 with linear correlation coefficients as high as 0.80-0.91 (p< 0.05). 353 354 Relatively high levels of Co (up to 59 mg kg-1), Sc (44.9 mg kg-1) and V (383 355 mg kg-1) were measured in the OMZ, whereas the lowest levels were found in soils of 356 the Guadalquivir Basin. The greatest abundances of Co, Sc and V in soils seem to be 357 related to the occurrence of underlying mafic igneous rocks, mainly basalts, gabros and 358 metabasites derived from basaltic lavas, particularly in the SPZ and OMZ zones. Hence, 359 their spatial distribution appears to be controlled by the parent rock lithology. 360 361 The extreme anomalies of Co, V and Sc in the OMZ occurred at the top of the 362 soils developed on the Acebuches amphibolites, in the Aracena metamorphic belt 363 (Castro et al., 1996). Relatively high concentrations of Co were also found in Leptosols 364 of the SPZ linked to acid volcanic and volcano-sedimentary parent rocks, in which the 365 VHMS deposits of the Iberian Pyrite Belt are hosted. A range of critical elements, 366 including Co may be contained in the base metal mineralization. 367 368 Antimony (Sb) 369 370 The total Sb content in topsoil samples varied largely from less than 0.1 mg kg-1 371 to 318 mg kg-1, with a median value markedly low (1 mg kg-1). Baseline concentrations 372 of Sb ranged up to 6.6 mg kg-1 in the SPZ and 4.5 mg kg-1 in the OMZ, exceeding 373 significantly those of the European soils. There is no apparent association with a 374 specific lithology in the distribution of Sb and it did not show a linear correlation in its 375 spatial distribution with any of the other analyzed elements. 376 16 377 The contents of Sb in the samples of the SPZ are widely spread from the mean 378 (16.2 ± 51.5 mg kg-1) due to its inhomogeneous distribution in topsoil. The highest Sb 379 concentrations (above 100 mg kg-1) were measured in Leptosols of the Iberian Pyrite 380 Belt, due to naturally occurring Sb-bearing sulfides and sulfosalts in mineralized 381 bedrock. They can be attributed not only to geogenic origin but probably also to diffuse 382 contamination associated with past mining activities. In fact, some mines were 383 historically worked for Sb (Leistel et al., 1998), which may occurs as locally dispersed 384 in soil. In the OMZ zone, the greatest abundances of Sb were found in topsoil formed 385 from weathering of carbonate rocks rather than igneous rocks or metasediments. There 386 is a good spatial correspondence between high concentrations of Sb in topsoil and 387 location of the Pb-Zn-Ag metallogenic belts of the OMZ zone (Tornos et al., 2004, 388 Fernández-Caliani et al., 2019). 389 390 Outlier and extreme values for Sb were also detected in peri-urban contaminated 391 soils of Huelva, one of the first industrial cities in Spain (Fernández-Caliani, 2012), 392 where the most obvious cause of the anomalous concentrations is anthropogenic. In 393 addition, an extreme Sb anomaly was identified in the Campo de Gibraltar Complex 394 that is difficult to explain without further investigation. 395 396 4.2 Vertical distribution of critical elements within the soil profile 397 398 Variability of elements concentrations within the soil profile was low. 399 Differences between the median values of the two soil sampling levels were relatively 400 small for most critical elements, as indicated by a ratio topsoil/subsoil from slightly 401 17 above the unity to 1.15, thus providing a lithological cause for most anomalies as the 402 concerned elements have limited mobility in soil. Exceptionally, Sb (1.25) and Co 403 (1.18) were found in greatest concentrations in topsoil relative to subsoil, most likely 404 due to anthropogenic contributions, although such surface enrichments require a high-405 density geochemical survey to trace their source. In fact, since some Co-bearing and Sb-406 bearing ore deposits have been mined historically in the region, it is difficult to evaluate 407 whether anomalies are natural in origin or mining has exacerbated the original mild 408 anomalies. 409 410 The concentrations of critical elements in topsoil and subsoil were positively and 411 strongly correlated, most notably for Sb, Sc, V, Hf and Co. The Pearson´s correlation 412 coefficients given in Figure 5 allowed us to evaluate the linear relationships between 413 topsoil and subsoil samples, and then the spatial variability in concentrations of critical 414 elements within the soil profile. Despite most REE are usually immobilized in 415 weathering resistant primary minerals (Galán et al., 2007), such as zircon, monazite, 416 xenotime, some topsoil samples appear to be REE-depleted. This is particularly true for 417 Ce, because Ce(III) can be easily oxidized to Ce(IV) under the oxidizing conditions 418 prevailing in the surface soil, and subsequently retained in subsoil onto clay minerals. 419 420 4.3 Some factors controlling the spatial distribution of anomalies 421 422 In an attempt to visualize the relationships between the abundance and spatial 423 distribution of the measured critical elements and the underlying geology, Figure 6 424 depicts graphically the percentage of anomalous concentrations of critical elements 425 according to the geological setting of the bedrock, lithology of the underlying parent 426 18 material and soil type. The observed distribution pattern of the mild and extreme 427 anomalies certainly reflects the influence of the local geology on soil geochemistry, and 428 especially the parent rock lithology and the occurrence of ore deposits hosting critical 429 elements in the survey area. 430 431 Based on the available data, it is apparent that the areas of greatest interest for 432 strategic metals in western Andalusia are found within the crystalline terranes of the 433 Iberian Massif (Fig. 6a). The CIZ is the main prospective zone for Be and W, the OMZ 434 contains promising areas for Co, Sc, V, Hf, Ta, and REE exploration, and the geological 435 setting of the SPZ appears favorable for prospecting for Sb and, to a lesser extent, Co, V 436 and Sc. Most of the anomalies of Be, W, Ta and REE are within the weathering crusts 437 of granites and soils developed on margins of granitic intrusive bodies, whereas the 438 most pronounced anomalies of Co, Sc and V were observed in soils derived from basic 439 and ultrabasic rock throughout the terranes of the Iberian Massif. The outlier values of 440 Hf and Sb were mostly found in soils on slates and schists, although a number of 441 threshold exceedances for Hf was also related to sandy soils of the Gudalquivir Basin 442 (Fig. 6b). Finally, the vast majority of geochemical soil anomalies were recorded in 443 Cambisols and Leptosols with little or no profile differentiation (Fig. 6c). 444 445 5. Conclusions 446 447 The soil sampling strategy used in this exploratory study has allowed us to 448 determine the geochemical baseline variation of selected critical elements in soil for 449 distinctive geological environments, to provide threshold values for anomaly detection, 450 19 and to explain the source and factors influencing the distribution of the major soil 451 geochemical anomalies. 452 453 Lithology of the underlying bedrock is inferred as the major source of 454 geochemical anomalies, although abundance and spatial distribution of critical elements 455 not only depends on the parent rock lithology, but also it is connected with local ore 456 deposits and occurrences of a vast range of mineralization styles. Soils over peralkaline 457 felsic igneous intrusions, distributed along tectono-magmatic alignments of the CIZ and 458 ZOM, are clearly marked by W, Be, Ta and REE anomalies, whereas the anomalous 459 concentrations of Sc, Co and V are closely associated with soils developed on mafic 460 igneous rocks of the ZOM and SPZ. The Hf and Sb anomalies seem to be related to 461 soils derived from pelitic metasediments. The distribution of high values of Sb and Co 462 is also related to well-known massive sulfide ore occurrences, notably in the Iberian 463 Pyrite Belt of the SPZ and in the metallogenic belts of the ZOM. Some spurious outliers 464 and extreme values of Sb and Co may have been affected by anthropogenic inputs. 465 466 Prospective areas for REE resources are locally identified in the Santa Olalla 467 Igneous Complex, where there is potential for forming REE deposits including ion-468 adsorbed type REE mineralization, residual primary and/or secondary REE-bearing 469 minerals in well-developed weathering profiles of tonalite rocks. The granodioritic 470 pluton of the Los Pedroches batholith and the plutonic-volcanic complex of Villaviciosa 471 de Córdoba-La Coronada may also represent interesting prospective targets for high-472 tech metals, and should be investigated at a more detailed scale. 473 474 Acknowledgments 475 20 476 The findings presented in this paper were obtained in the framework of the 477 Project “A Survey of Trace Element Concentrations in Soils of Andalusia”, a research 478 program led by Prof. Emilio Galán and financially supported by the Andalusia 479 Government (Spain). 480 481 References 482 483 Bao, Z., Zhao, Z. 2008. Geochemistry of mineralization with exchangeable REY in the 484 weathering crusts of granitic rocks in South China. Ore Geol. Rev. 33, 519-535. 485 486 Carranza, E.J.M., 2009. Geochemical Anomaly and Mineral Prospectivity Mapping in 487 GIS. Handbook Exploration and Environmental Geochemistry, Vol. 11, Elsevier. 488 489 Castro, A., Fernández, C., De la Rosa, J.D., Moreno-Ventas, I., Rogers, G., 1996. 490 Significance of MORB-derived amphibolites from the Aracena Metamorphic Belt. J. 491 Petrol., 37, 235-260. 492 493 Donaire, T., Pascual, E., Pin, C., Duthou, J.L., 1999. Two-stage granitoid-forming event 494 from an isotopically homogeneous crustal source: The Los Pedroches batholith, Iberian 495 Massif, Spain. Geol. Soc. Am. Bull. 111, 1897-1906. 496 497 Ercit, T.S., 2005. REE-enriched granitic pegmatites. In: Linnen, R.L., Samson, I.M. 498 (Eds), Rare-Element Geochemistry and Mineral Deposits. Geol. Ass. Canada, pp. 175-499 199. 500 21 501 European Commission, 2017. Study on the Review of the List of Critical Raw 502 Materials: Criticality Assessments. Final Report, http://doi.org/10.2873/876644 503 504 Fernández-Caliani, J.C., 2012. Risk-based assessment of multimetallic soil pollution in 505 the industrialized peri-urban area of Huelva, Spain. Environ. Geochem. Health, 34, 123-506 139. 507 508 Fernández-Caliani, J.C., Giráldez, M.I., Rivera, M.B., 2019. Source and geochemical 509 partitioning of silver in a naturally-enriched soil. Appl. Geochem. 103, 85-96. 510 511 Galán, E., Fernández-Caliani, J.C., Miras, A., Aparicio, P., Márquez, M.G., 2007. 512 Residence and fractionation of rare earth elements during kaolinization of alkaline 513 peraluminous granites in NW Spain. Clay Min. 42, 341-352. 514 515 Galán, E., Fernández-Caliani, J.C., González, I., Aparicio, P., Romero, A., 2008. 516 Influence of geological setting on geochemical baselines of trace elements in soils. 517 Application to soils of South-West Spain. J. Geochem. Expl. 98, 89-106. 518 519 García-Cortés, A. (Ed.), 2011. Cartografía de Recursos Minerales de Andalucía. 520 Instituto Geológico Minero de España - Consejería de Economía, Innovación y Ciencia 521 de la Junta de Andalucía. 522 523 Gibbons, W., Moreno, T., (Eds.), 2002. The Geology of Spain. The Geological Society, 524 London. 525 22 526 Graedel, T.E., Harper, E.M., Nassar, N.T. Nuss, P., Reca, B.K., 2015. Criticality of 527 metals and metalloids. PNAS, 112, 4257-4262. 528 529 Hayes, S.M., McCullough, E.A., 2018. Critical minerals: A review of elemental trends 530 in comprehensive criticality studies. Resour. Policy, 59, 192-199. 531 532 ISO (International Organization for Standardization), 2005. Soil Quality - Guidance on 533 the Determination of Background Values. International Standard ISO 19258: 2005(E) 534 24 pp. 535 536 Jowit, S.M., Wong, V.N.L., Wilson, S.A., Gore, O. 2017. Critical metals in the critical 537 zone: controls, resources and future prospectivity of regolith-hosted rare earth elements. 538 Austral. J. Earth Sci., 64, 1045-1054. 539 540 Julivert, M., Fontboté, J.M., Ribeiro, A., Conde, L., 1972. Mapa Tectónico de la 541 Península Ibérica y Baleares a escala 1:1.000.000. Memoria explicativa. IGME, Madrid. 542 543 Leistel, J.M., Marcoux, E., Thiéblemont, D., Quesada, C., Sánchez, A., Ruiz de 544 Almodóvar, G., Pascual, E., Sáez, R., 1998. The volcanic-hosted massive sulphide 545 deposits of the Iberian Pyrite Belt. Miner. Deposita 33, 2-30. 546 547 Li, Y.H.M., Zhao, W.W., Zhou, M.F., 2017. Nature of parent rocks, mineralization 548 styles and ore genesis of regolith-hosted REE deposits in South China: An integrated 549 genetic model. J. Asian Earth Sci. 148, 65-95. 550 23 551 Locutura, J., Bel-Lan, A., García-Cortés, A., Martínez, S., 2012. Atlas Geoquímico de 552 España. Instituto Geológico y Minero de España, Madrid. 553 554 Locutura, J., Tornos, F., Florido, P., Baeza, L., 1990. Ossa-Morena Zone: Metallogeny. 555 In: Martinez, E., Dallmeyer, R.D. (Eds), Pre-Mesozoic Geology of Iberia. Springer 556 Verlag, pp. 321-332. 557 558 Négrel, P., Ladenberger, A., Reimann, C., Birke, M., Demetriades, A., Sadeghi, M., 559 2019. GEMAS: Geochemical background and mineral potential of emerging tech-560 critical elements in Europe revealed from low-sampling density geochemical mapping. 561 Appl. Geochim. 111, 104425. doi.org/10.1016/j.apgeochem.2019.104425 562 563 Pascual, E., Pérez-Lorente, F., 1987. La alineación o eje magmático Villaviciosa de 564 Córdoba-La Coronada. In: Bea, F., Carnicero, A., Gonzalo, J.C., López-Plaza, M., 565 Rodríguez-Alonso, M.D. (Eds), Geología de los Granitoides y Rocas Asociadas del 566 Macizo Hespérico. Rueda, Madrid, pp. 365-376. 567 568 Reimann, C., De Caritat, P., 1998. Chemical Elements in the Environment. Springer-569 Verlag, Berlin. 570 571 Reimann, C., De Caritat, P., 2017. Establishing geochemical background variation and 572 threshold values for 59 elements in Australian surface soil. Sci. Total Environ. 578, 573 633-648. 574 575 24 Reimann, C., Filzmoser, P., Garret, R.G., 2005. Background and threshold: critical 576 comparison of methods of determination. Sci. Total Environ. 346, 1-16. 577 578 Romeo, I., Capote, R., Tejero, R., Lunar R., Quesada, C., 2006. Magma emplacement in 579 transpression: The Santa Olalla Igneous Complex (Ossa-Morena Zone, SW Iberia). J. 580 Struct. Geol. 28, 1821-1834. 581 582 Rudnick, R.L., Gao, S., 2004. Composition of the Continental Crust. In: Holland, H.D., 583 Turekian, K.K. (Eds), Treatise on Geochemistry, Elsevier, Amsterdam, Vol. 3, pp. 1-64. 584 585 Sáez, R., Almodóvar, G.R., Pascual, E., 1988. Mineralizaciones estratoligadas de 586 scheelita en la Faja Pirítica del Suroeste Ibérico. Bol. Soc. Esp. Min. 11, 135-141. 587 588 Sáez, R., Requena, A., Fernández-Caliani, J.C., Almodóvar, G.R., 1989, Control 589 estructural de las mineralizaciones de Sn-W-As del Bajo Corumbel, La Palma del 590 Condado, Huelva. Stvdia Geol. Salmant. Vol. Esp. 4, 189-203. 591 592 Salminen, R., (Ed.), 2005. Geochemical Atlas of Europe. Part 1: Background 593 Information, Methodology and Maps. Geological Survey of Finland. 594 http://www.gtk.fi/publ/foregsatlas 595 596 Sierro, F.J., González-Delgado, J.A., Dabrio, C., Flores, J.A. y Civis, J., 1996. Late 597 Neogene depositional sequences in the forelandbasin of Guadalquivir (SW Spain). In: 598 Friend, P.F., Dabrio, C.J., (Eds), Tertiary basins of Spain, the stratigraphic record of 599 crustal kinematics. Cambridge Univ. Press, pp. 339-345. 600 Element (mg kg-1) 95th Percentile 98th Percentile Outliers (Q3+1.5IQR) Number of mild anomalies Far outliers (Q3+3IQR) Number of extreme anomalies TOPSOIL Be 4 5 - 12 - 6 Co 32 41 33 14 48 4 Hf 19 26 19 12 28 3 Sb 8.4 24.2 4.7 20 7.1 18 Sc 28.8 34.6 27.9 15 40.4 2 Ta 2.1 2.8 2.6 9 4.1 0 V 193 247 202 11 293 1 W 5.0 8.9 - 12 - 7 La 67.7 80.4 78 6 111 2 Ce 139 154 159 4 227 1 Nd 56 63 64 4 91 2 Sm 11.2 13.5 12.1 9 16.9 0 Eu 2.3 2.9 2.4 12 3.3 3 Tb 1.40 1.69 1.69 6 2.55 1 Yb 5.8 7.2 6.8 8 9.6 1 Lu 0.91 1.17 1.02 9 1.44 1 Y 37 44 34 17 47 4 SUBSOIL Be 4.2 6.5 - 6 - 5 Co 32 40 32 16 47 4 Hf 22 24 19 10 28 2 Sb 6.3 16.3 2.9 13 4.2 15 Sc 26.1 31.9 27.3 9 49.9 0 Ta 2.0 3.3 2.4 5 3.7 2 V 175 196 204 3 299 0 W 6.0 9.0 - 7 - 4 La 71.7 90.6 71.1 11 100.3 0 Ce 139 161 143 9 201 0 Nd 56 69 56 10 78 1 Sm 11.3 14.7 11.5 8 16.1 2 Eu 2.1 2.5 2.6 4 3.6 0 Tb 1.40 1.50 1.63 3 2.45 1 Yb 6.2 7.2 6.1 10 8.6 3 Lu 0.97 1.19 0.95 9 1.35 3 Y 40 47 32 10 46 6 Table 3 Click here to download Table: Table 3.docx Economic importance (2.8) Supply risk (1.0) Economic importance Supply risk 5 0 1 2 3 4 5 6 7 Critical elements analyzed in this study Other critical elements and minerals Sb LREE (La,Ce,Nd,Sm,Eu) Sc Be V Hf Co W HREE (Tb,Yb,Lu,Y) Ta Mg P Bi Nb PGM Fluorspar Ga Ge Baryte In Graphite Borate 4 3 2 1 0 Figure 1 Click here to download Figure: Figure 1 .pptx Huelva Sevilla Cádiz Córdoba Central-Iberian Zone Ossa-Morena Zone South-Portuguese Zone Guadalquivir Basin External Betic Zone Campo de Gibraltar Complex Iberian Massif Betic Cordillera 25 km SPAIN PORTUGAL FRANCE Andalusia LEGEND Sampling site Province capital Province boundary Los Pedroches Batolith Figure 2 Click here to download Figure: Figure 2.pptx LEGEND Central-Iberian Zone Ossa-Morena Zone South-Portuguese Zone Iberian Massif Betic Cordillera Guadalquivir Basin External Betic Zone Campo de Gibraltar Complex Intrusive rocks Extremeanomalies >48mgkg‐1 Mildanomalies 33‐48mgkg‐1 Co HUELVA SEVILLA CÓRDOBA CÁDIZ 50km HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >7.1mgkg‐1 Mildanomalies 4.7‐7.1mgkg‐1 Sb HUELVA SEVILLA CÓRDOBA CÁDIZ 98thpercen le >5.3mgkg‐1 95thpercen le 3.7‐5.3mgkg‐1 Be HUELVA SEVILLA CÓRDOBA CÁDIZ 98thpercen le >8.9mgkg‐1 95thpercen le 5.0‐8.9mgkg‐1 W HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >293mgkg‐1 Mildanomalies 202‐293mgkg‐1 V Figure 3 Click here to download Figure: Figure 3.pptx HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >111mgkg‐1 Mildanomalies 78‐111mgkg‐1 La HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >227mgkg‐1 Mildanomalies 159‐227mgkg‐1 Ce HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >91mgkg‐1 Mildanomalies 64‐91mgkg‐1 Nd HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >16.9mgkg‐1 Mildanomalies 12.1‐16.9mgkg‐1 Sm Extremeanomalies >3.3mgkg‐1 Mildanomalies 2.4‐3.3mgkg‐1 Eu 19 HUELVA SEVILLA CÓRDOBA CÁDIZ HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >2.55mgkg‐1 Mildanomalies 1.69‐2.55mgkg‐1 Tb HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >9.6mgkg‐1 Mildanomalies 6.8‐9.6mgkg‐1 Yb HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >1.44mgkg‐1 Mildanomalies 1.02‐1.44mgkg‐1 Lu HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >47mgkg‐1 Mildanomalies 34‐47mgkg‐1 Y HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >40.4mgkg‐1 Mildanomalies 27.9‐40.4mgkg‐1 Sc HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >28mgkg‐1 Mildanomalies 19‐28mgkg‐1 Hf HUELVA SEVILLA CÓRDOBA CÁDIZ Extremeanomalies >4.1mgkg‐1 Mildanomalies 2.6‐4.1mgkg‐1 Ta Felsic igneous rocks Mafic igneous rocks Sb W Eu Yb Lu Be Y Hf Ta V -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 Factor 1 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 Factor 2 Sb Sc W La Nd Sm Tb Be Y Hf Ta Co Ce RARE EARTH ELEMENTS Figure 4 Click here to download Figure: Figure 4.pptx 1 10 100 1000 1 10 100 1000 La 0 200 400 600 800 1000 0 50 100 150 200 250 Ce r= 0.58 0 100 200 300 400 0 50 100 150 Nd r= 0.64 0 10 20 30 40 50 60 0 5 10 15 20 Sm r= 0.62 N= 268 N= 270 N=260 N=269 0 1 2 3 4 0 1 2 3 4 Tb r= 0.72 N= 259 N= 72 0 5 10 15 0 5 10 15 0 0.5 1 1.5 2 2.5 -0.5 0.5 1.5 2.5 Lu r= 0.76 N= 263 Yb r= 0.76 N= 266 Subsoil (mg kg-1) Topsoil (mg kg-1) Subsoil (mg kg-1) Subsoil (mg kg-1) Subsoil (mg kg-1) Subsoil (mg kg-1) Subsoil (mg kg-1) Subsoil (mg kg-1) Subsoil (mg kg-1) Topsoil (mg kg-1) Topsoil (mg kg-1) Topsoil (mg kg-1) Topsoil (mg kg-1) Topsoil (mg kg-1) Topsoil (mg kg-1) Topsoil (mg kg-1) r= 0.62 0 1 2 3 4 5 6 -1 1 3 5 r= 0.73 Eu Figure 5 Click here to download Figure: Figure 5.pptx 0 100 200 300 400 0 100 200 300 400 0 10 20 30 40 50 0 10 20 30 40 50 0.1 1 10 100 1000 0.1 1 10 100 1000 0 20 40 60 80 0 20 40 60 80 Co V r= 0.75 r= 0.79 Sb r= 0.91 Sc r= 0.81 N= 327 N= 202 N= 252 N= 270 0 20 40 60 80 100 120 0 20 40 60 80 100 120 Y r= 0.51 N= 269 Subsoil (mg kg-1) Topsoil (mg kg-1) Subsoil (mg kg-1) Topsoil (mg kg-1) Subsoil (mg kg-1) Topsoil (mg kg-1) Subsoil (mg kg-1) Topsoil (mg kg-1) Subsoil (mg kg-1) Topsoil (mg kg-1) 0 10 20 30 40 50 0 20 40 60 N= 195 Subsoil (mg kg-1) Topsoil (mg kg-1) r= 0.77 Hf 0 10 20 30 40 50 60 70 80 Be W Hf Ta V Co Sb Sc LREE HREE CIZ OMZ SPZ GB BC CGC % Central Iberian Zone (CIZ) Ossa-Morena Zone (OMZ) South-Portuguese Zone (SPZ) Guadalquivir Basin GB) Betic Cordillera (BC) Campo de Gibraltar Complex (CGC) a Figure 6 Click here to download Figure: Figure 6.pptx