Mineralogy and geochemistry of bottom sediments from water reservoirs in the vicinity of Córdoba, Argentina: Environmental and health constraints

Applied Clay Science 36 (2007) 206 – 220 www.elsevier.com/locate/clay

Mineralogy and geochemistry of bottom sediments from water reservoirs in the vicinity of Córdoba, Argentina: Environmental and health constraints Silvana R.A. Bertolino a,⁎, Udo Zimmermann b , Federico J. Sattler c a

CONICET, Facultad de Matemática, Astronomía y Física, Ciudad Universitaria, (5016) Córdoba, Argentina b University of Johannesburg, Department of Geology, 2006 Auckland Park, Johannesburg, South Africa c Facultad de Matemáticas, Astronomía y Física, Ciudad Universitaria, (5016) Córdoba, Argentina Received 8 May 2006; received in revised form 16 June 2006; accepted 24 June 2006 Available online 13 October 2006

Abstract The lake sediments display a typical upper crustal composition and include a less fractionated component related to the closely exposed Cambrian continental arc. No basic source component could be detected. The sediments are strongly chemically weathered (K/Cs b 2000; CIA 70–80) and depleted in most of the major and trace elements. The depositional environment is characterised by oxidising conditions regarding geochemical constraints and facies conditions. Only U (5–15 ppm), W (9–21 ppm) and As (5–22 ppm) are strongly enriched trace elements related to the post-Archaean average Australian shale or upper crust. This enrichment is explained as related to mining activities and mineralisation. W and U mines are common in closest vicinities. The enrichment in U does not reflect the concentrations in the mined bodies, thus, the loss of U during transport and sedimentation was most probably buffered by sediments deposited under anoxic conditions and/or plants. Those trace metal element traps may contain much higher element abundances as the sediments here discussed. This preliminary study conducted with simple, quick but effective methodology shows alarming concentrations of trace metals in sediments, although the selected sediments are not the most likely to concentrate elements like U. This implies that suitable sediments and sedimentation areas have to be determined carefully by comprehensive fieldwork and guided by the understanding of the local drainage systems. If this is ignored, a reliable study, which excludes contamination, cannot be conducted. Based on our preliminary studies, the water, sediments and flora should not be used for human purposes until contamination sources and flux is entirely understood, which is not the case for this highly contaminated zone so far. © 2006 Elsevier B.V. All rights reserved. Keywords: U–W–As contamination; Lake sediments; Provenance

1. Introduction ⁎ Corresponding author. Facultad de Matemáticas, Astronomía y Física, Universidad Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria (5000), Córdoba, Argentina. Fax: +54 351 4334054. E-mail addresses: [email protected] (S.R.A. Bertolino), [email protected] (U. Zimmermann). 0169-1317/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2006.06.011

During the last decades many efforts have been made to evaluate the environmental conditions of soils and water resources close to mining areas, as well as to understand the transfer of inorganic pollutants to soil and water and from them to the food chain. Damage

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caused especially by trace metals is widely investigated and their effects cannot be underrated especially that long-term damage is not yet well understood, but occurs frequently elsewhere. The Pampean Ranges of Córdoba, Argentina, have several ore districts, most of them not currently exploited. In Sierras Grandes (Fig. 1) mainly U, W and Be were mined but also Au, Nb, Ta and Cr are mineralised in significant concentrations. In Pampa de Oláen W district, Los Guindos mines (Fig. 1), contain also Cu, Sn, Bi, Pb, Mo, Fe and sulphide mineralisation (Gamba, 1999); in Punilla (N), Santa María and Calamuchita (S) districts, Cu, Cu–Fe and Pb–Zn mines are enriched in As among other elements (Mutti and Di Marco, 1999). The mines occur within the catchment drainage basin of the water reservoirs San Roque (SR) and Los Molinos (LM) (Fig. 1). These water reservoirs provide drinking water to the main cities and villages in the region, and the province capital city of Córdoba, which means a total population of ca.

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1,500,000. The U mining was mostly developed until 1990 while the others until 1950s and 1960s, when environmental regulations were still lax, resulting in an environmentally harmful accumulation of solids and wastes of low-grade ore and gangue. In addition, the sparse Tertiary sedimentary rocks are also enriched in uranium (Bertolino and Zimmermann, 2006). Early Tertiary sedimentary rocks fill the fault-bounded Punilla valley (Fig. 1) and crop out at its eastern border (Lencinas, 1971). They are dissected by the north–south trending San Francisco and Cosquín rivers that drain from the north into the SR reservoir. About 10 km north of the mouth of the Cosquín river, in the vicinities of Cosquín, these sedimentary successions bear a conspicuous uranium–vanadium mineralisation (Mina Rodolfo) (Fig. 1). The U mines are located within the Achala Batholith that represents about half of the area of interest in this paper. Los Gigantes uranium mine still has large leaching pads at the sites. When active, they were pouring the

Fig. 1. Location map showing the general geology, sampling and main mining sites.

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liquid wastes, containing acids, metals and residual uranium compounds to the neighbouring streams and into the Cajón river (the main catchment area along with the Icho Cruz river, Ugarte, 2006), tributary of the San Antonio river that discharges from the south into the SR reservoir. The spills continued and continue after closing the mine, during the rainy summer seasons. The mine is now under the Uranium Mining Environmental Restoration Project (PRAMU) of the National Nuclear Energy Commission of Argentina (CNEA, 2006); they analysed the U concentration of wastes and tailings (59–217 ppm) and the activity concentration of 226 Ra (0.6–1.2 Bq g− 9) and Rn (0.21–0.33 Bq/m2 s) radiation. They also reported that the tailings have a pH of 4.85, contain 25–35% SO4, 74% P2O5, and rather elevated contents of Cu, up to 100 ppm, Cr 150 ppm, V 100–200 ppm and Zn 300–600 ppm. Several of the mentioned elements from local ore deposits are of strongest health concerns. The Agency for Toxic Substances and Disease Registry of USA reported that all uranium complexes can cause damaged kidneys. Moreover, and more compelling, it is common sense that elevated U concentrations are triggering mutations in organic tissue, and humans as well, as observed elsewhere (ATSDR, 1999). W, though not very dangerous, may cause breathing problems and changes in behaviour if exposed to large amounts (ATSDR, 2005a). Arsenic, common in sulphides present in ore deposits, is of great concern in Argentina because of the high levels detected in subsurface waters from the Chaco–Pampean plain (Nicolli et al., 1985; Hopenhayn, 2006). It is the first element in the top twenty hazardous substances in the priority list of 2005 made by the CERCLA (Comprehensive environmental Response, Compensation, and Liability Act; ATSDR, 2005b,c), causing cancer and other diseases, like the skin disorder known as “Bell Ville Disease”, named after the city of Bell Ville in southern Córdoba province. Environmental concern is growing in the region but there is still a lack of information related to the impact of mining in the area, although the uranium mining is considered to be one of the environmental hazards in the region (as reported by the Comisión Permanente para la Prevención y el Control de la Contaminación in 1987, and in internal reports of the FUNAM Foundation). Several investigations were dealing with water quality, nutrients content and the eutrophic processes at LM and SR reservoirs related to agriculture and urban contamination (Sattler, 2003; Rodríguez, 2003; Oroná, 2004, and the papers cited therein). The investigations related to the reservoirs report evidences of eutrophication revealed by oxygen deple-

tion at the hypolimnium, increment of nutrients, excessive growing of cyanophyte and dinoflagelate algae, suggesting that in 20 years the LM reservoir will reach a mesotrophic state if the process and conditions continue as today, while the SR reservoir may change its actual eutrophic state into a hypertrophic one. The Oroná (2004) study was concentrated on nutrients (P) and organic pollutants and their relation to bottom-lake sediments. Sattler (2003) studied the bulk and clay fraction mineralogy and texture of the reservoirs' bottom sediments and soils developed on the different regional lithologies, considering their environmental significance related to P and nutrients contents and to understand the character of probable trace metal traps. In this paper, the geochemistry and provenance of bottom-lake sediments from the SR and LM water reservoirs, located at the Eastern Pampean Ranges of Córdoba, Argentina, were studied and their mineralogy revised. This can lead to an understanding of the most probable host sediments of trace metals and can propose detailed and comprehensive sampling strategies. Furthermore, this study can supply a preliminary evaluation of the impact of the mining and ore deposits located in the surroundings on the water reservoirs. 2. Basins and reservoir characteristics Both reservoirs are located in the fault-bounded valleys (Fig. 1) limited by the Sierras Chicas (east) and Sierras Grandes (west), the SR in the Punilla valley (north) and LM in the Calamuchita valley (south). Both are important areas of tourist interest. The SR basin covers a surface of 1750 km2; the Cosquín (N) and the San Antonio (S) rivers catchment areas represent 54% and 32% of the basin, respectively. The lake extends over 24.78 km2, with a maximum depth of 35.3 m and a mean depth of 14.1 m. The first dam was built in 1890 and the second in 1949, as a hydroelectric press, to provide drinkable water to Córdoba and is used for recreation. The LM basin has a total surface of 894 km2; from north to south the San Pedro (10.7%), Los Espinillos (38%), del Medio (14.7%) and Los Reartes (25%) rivers feed the reservoir. The lake surface is 21.1 km2, maximum depth of 53 m and mean depth of 16.3 m. It was built in 1953 to generate electricity, to provide drinkable water and is used for recreation too. The weather in the region is temperate, continental with semiarid tendency; annual rainfall is highly seasonal and torrential of about 900 mm at Sierras Grandes decreasing north-eastward to 600 mm; due to global change there has been an increment of about 10%

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in the last decades. The spring–summer is the rainy season provoking sudden floods of considerable magnitude (Ugarte, 2006). Upper catchments of the rivers discharging their waters into lakes, are located in the Sierras Grandes (∼ 2000 m a.s.l.), except for the San Francisco river, a tributary of the Cosquín river, that runs from north to south along the Punilla valley. The area belongs to the Sierras Pampeanas geological province mainly composed of Proterozoic and Palaeozoic crystalline basement rocks, comprising of medium- to high-grade metamorphic rocks and granites of the Achala Batholith (Gordillo and Lencinas, 1979). Metamorphic rocks occupy large areas particularly in the LM basin and are represented by tonalitic gneiss (oligoclase, quartz, biotite, subordinate garnet and sillimanite), cordieritic gneiss (plagioclase, quartz, garnet, cordierite, biotite and minor alkali feldspar), amphibolites, metagabbro (plagioclase, ortho- and clinopyroxene, hornblende, biotite) and marbles. The most extensive granite facies is a porphyric monzogranite, comprising quartz, albite, megacrystals of microcline, minor biotite and muscovite (Lira and Kirschbaum, 1990). Eocene to Miocene sedimentary rocks, the Punilla Group, fill the Punilla valley and crop out at the Sierras Chicas slope. The group

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comprises two formations, the Cosquín Formation with sandstone and mineralised shales, bearing uranium/ vanadium mineralisations of mainly carnotite and tyuyamunite, and the Casa Grande Formation with polymictic fanglomerates comprising lithic clasts and blocks of predominantly granitic composition (Lencinas, 1971). Finally, loess-like Quaternary sediments are restricted to high plains and valleys. 3. Materials and methods Bottom sediment samples from each reservoir were collected near the mouths of the main tributaries (SR1: San Antonio; SR3: Cosquín; LM1: Los Reartes and del Medio; LM4: Los Espinillos; LM5: San Pedro), at the centre (SR2; LM2) and near the dams — gorge — (SR5; LM6), with a stainless steel Ekman type dredge. They vary from sand or sandy loams close to the rivers mouths to clayey loams in the centre and gorge. A sample (CB) was obtained at Cuesta Blanca (the first urban settlement by the river) from the suspended load of the San Antonio River during an unusual – but frequent during the 1980s – light-coloured flood that happened in January 1989, when the Los Gigantes U mine was still active. One sample from the Rodolfo Mine (MR) was also taken for mineralogical analyses. Mineralogical studies were conducted by optical methods (both petrographic microscope and binocular) on the coarse fraction, and by X-ray diffraction (XRD). XRD analyses were applied on the bulk and the b 2 μm clay fraction in random and oriented mounts (air dried, glycolated and heated to 375 °C and 550 °C) using a PW1710 BASED diffractometer with CuKα radiation at 40 kV and 30 mA, step size 0.02°. The Kübler illite crystallinity index, IC (width of (001) reflection at half height in grad 2θ), was measured on the glycolated XRD pattern (Warr and Rice, 1994). Major, minor, trace and rare earth elements (REE) were determined on the bulk material (SR5, LM6) and the b 2 μm fraction (SR5 b 2, LM6 b 2) of samples from the gorge of each reservoir. Analyses were performed at Activation Laboratories LTD., Canada, by combined lithium metaborate/ tetraborate fusion ICP and trace element ICP/MS method (details of the procedures are found in www.actlabs.com).

4. Results 4.1. Mineralogy

Fig. 2. XRD patterns of bulk samples from San Roque reservoir. M: micas, Gy: gypsum, K: kaolinite, Gib: gibbsite, Op: opal, Mi: microcline, Pl: plagioclase, Chl: chlorite, Ty: tyuyamunite, Qz: quartz, Car: carnotite, Ph: phyllosilicates, He: hematite, Hol: hollandite, F: feldspars, Py: pyrophillite.

4.1.1. Basin The soils developed from granitic rocks are composed of quartz, plagioclase, microcline, muscovite, biotite and scarce kaolinite (compiled from Sattler, 2003). Within the clay fraction, illite prevails; I/S (20–30% I, R0) and kaolinite occur in minor proportions along with traces of goethite and opal-C. Soils developed from metamorphic rocks usually contain quartz and oligoclase, with minor

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The main component of the clay fraction is illite associated with I/S (20–30% I, R0) and minor amounts of chlorite, kaolinite, and C/S (70% C, R0). Pedogenesis is stronger in soils from the Calamuchita valley, where usually interstratified minerals are more abundant in the clay fraction.

Fig. 3. XRD patterns of b2 μm EG-saturated samples from San Roque reservoir. I/S: illite/smectite, Ill: illite, K/S: kaolinite/smectite, Goe: goethite, C/S: chlorite/smectite.

micas and hornblende and traces of chlorite and kaolinite. Illite, I/S (20–30% I, R0), chlorite, C/S, kaolinite and traces of Al-hydroxides and goethite are the main constituents in the clay fraction. Sample MR, shales of the Cosquín Formation at Mina Rodolfo (Fig. 2), comprises quartz, plagioclase, tyuyamunite, carnotite, muscovite, biotite and chlorite.

Fig. 4. XRD patterns of bulk samples from Los Molinos reservoir. Px: pyroxene, Grt: garnet, Horn: hornblende, Olig: Oligoclase, Ap: fluorapatite, others as in Fig. 2.

4.1.2. San Roque reservoir The bulk mineralogy of sediments from the mouths of the two rivers mainly differs in minerals proportions (Fig. 2). SR1 (San Antonio imput) contains some pyrophyllite while SR3 (Cosquín imput) bears tyuyamunite and traces of carnotite. Otherwise, both have essential plagioclase N quartz N microcline N biotite and muscovite, minor amounts of chlorite, kaolinite, illite/smectite (I/S), garnet, and traces of hematite. SR2 (centre) and SR5 (gorge) phyllosilicates (illite, chlorite and kaolinite) prevail over quartz, albite–oligoclase and microcline. Goethite, gibbsite and traces of tyuyamunite are also present. The clay mineralogy is similar in all samples but differ in crystallinity and proportions. It is characterised (Fig. 3) by illite N irregular I/S (20–30% I, N80–90% I R0) ≫ kaolinite N chlorite ≫ kaolinite/smectite (K/S), chlorite/smectite (C/S, 70–90% C). However, feldspar and quartz are minor components, and goethite, Alhydroxides as well as opal-C are scarce. Traces of hollandite are present in samples SR3, SR2 and SR5. Kaolinite is more abundant than chlorite in the south; I/S is better defined in the centre of the lake. There is a

Fig. 5. XRD patterns of EG-saturated samples from Los Molinos reservoir. References as in Fig. 3.

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general trend to higher IC values towards the gorge (from 0.26–0.44° to 0.54–0.68°), where the fine clay fraction (b 1 μm) concentrates, but it may suggest that the clay minerals are being degraded in deeper zones. The main input of chlorite, C/S and U–V minerals comes from the Cosquín and San Francisco catchment areas. The sample CB from the suspended load of the San Antonio flood has very well crystallised kaolinite and illite (IC 0.22), opal-C and gibbsite in similar proportions with accessory plagioclase, K-feldspars, chlorite, calcite and gypsum. This mineral suite does not reflect the mineralogy of regional soils where kaolinite is merely a minor component; opal occurs in traces. Illite and kaolinite have low crystallinity (IC ∼ 0.50–0.70). The mineral composition reflects that of the U mineralisation at Los Gigantes mine. The deposit is a stockwork produced by hydrothermal alteration. Paragenetic clays comprises illite, kaolinite, montmorillonite and I/S (Blasón, 1999), and opal (hyalite) in U bearing epysienites from neighbouring areas (Lira, 1987). 4.1.3. Los Molinos reservoir The sediments are characterised by the occurrence of minor concentrations of hornblende, garnet, cordierite, all derived from the local metamorphic rocks (Fig. 4); main components are quartz N plagioclase ≫ microcline, muscovite, biotite and accessory chlorite and kaolinite. Fluorapatite and oligoclase are present in sample LM1 at Los Reartes and del Medio rivers mouths, where microcline is more abundant compared with the other samples. Like in SR, micas and phyllosilicates prevail in the centre and gorge. The clay mineralogy is similar in all samples (Fig. 5), with illite ≫ I/S (20–30% I N 80–90% I R0), minor chlorite, kaolinite, C/S (∼70% C) and goethite, low amounts of quartz, albite–oligoclase and occasionally hornblende. Mixed layer minerals are more abundant than in the SR lake. Differences in mineralogy or mineral abundance are negligible. IC values are high and do not change (IC 0.72–0.81); the highest is found at the mouth of Los Espinillos river. This fact represents an important difference to the previously discussed reservoir. 4.2. Geochemistry 4.2.1. Major element geochemistry The sampled sediments are generally low in Si and Ca but have high LOI, which can be explained by the relatively high amount of organic matter (SR5, 16.18%; LM6, 15.58%). The samples from both lakes are only

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slightly different, as those from SR are enriched in Al, Mg, Fe, Na and K, but all other major element contents are roughly similar. The finer fraction (b2 μm) is in general enriched in major element besides Si and Ti. Na is depleted in lake LM, while the sample from SR is enriched in Na in relation to the coarser sediments (Table 1). In comparison to PAAS (post-Archaean Australian average shale after Taylor and McLennan, 1985) the samples are mainly depleted in all major elements except Fe, Mn and P. 4.2.2. Alteration and weathering trends The use of major element geochemistry, in particular, should be treated with the greatest caution due to the possible mobility of these elements and their redistribution during chemical weathering and diagenesis (e.g. Nesbitt, 2003). However, it can be used partly to determine the degree of alteration of the source material (Nesbitt and Young, 1982; Fedo et al., 1995; von Eynatten et al., 2003). The Chemical Index of Alteration (CIA = molar [Al2O3/Al2O3 + CaO⁎ + Na2O + K2O] × 100, where CaO⁎ is CaO in silicates only; Nesbitt and Young, 1982) provides a mean to determine the degree of weathering of detritus constituting the sedimentary rock. K and Cs are mostly adsorbed onto clay minerals during weathering. Cs, the larger ion, is favourably adsorbed above K (in particular by illitic minerals). The K/Cs ratio should therefore increase with decreasing chemical weathering. The relationship between Th/U ratio and Th concentration can also be applied as an estimate of the degree of weathering in sedimentary rocks. Both Th and U are relatively immobile during weathering, although U may change its redox state during reworking under aerobic conditions and is thus more readily removed from the system, thereby increasing the Th/U ratio above upper crustal igneous values of 3.5–4.0 (McLennan et al., 1993). Fig. 6a shows the relation between K/Cs ratios and the CIA. The latter is high with values between 70 and 83 (Table 1). Interestingly, the fine fraction of LM displays a clearly higher CIA than the sediments of SR, which is also reflected by the high IC values and the higher contents of mixed layer clay minerals. The strong chemical weathering is reflected in low K/Cs ratios as well (Fig. 6a), as these are lower than PAAS (2050, after Taylor and McLennan, 1985) and UCC (upper continental crust 6100, after McLennan, 2001). Moreover, the assigned main source of the sediments, the Achala granite, displays K/Cs around 8500 (Table 2), and absolute lower Cs concentrations (4.9 ppm) than the sampled sediments (Table 1).

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Table 1 Major and trace element concentrations of the lake sediments

SiO2 Al2O3 Fe2O3(T) MnO MgO CaO Na2O K2O TiO2 P2O5 CIA LOI Total Ba Rb Sr Cs Cr V Co Ni Cu W Zn Ga As Nb Ta Y Zr Hf Pb Th U Sc Mo La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ∑REE

% % % % % % % % % % % % ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

LM6

LM6 b 2 μm

SR5

SR5 b 2 μm

53.57 12.95 6.05 0.14 1.89 1.06 0.79 2.08 0.67 0.21 70 19.5 99.0 383 137 94 11.2 50 96 21 30 50 21.0 130 25 b5 12.0 1.1 24.0 90 3.2 13 10.6 5.6 11.0 b2 29.9 63.3 7.2 27.2 5.8 1.3 5.3 0.8 4.6 0.9 2.6 0.38 2.4 0.34 152

48.72 14.54 6.86 0.17 2.07 0.94 0.41 2.00 0.62 0.25 80 23.3 99.9 352 135 63 11.1 50 104 25 20 50 9.0 50 26 18 10.0 1.1 27.0 64 2.8 b5 11.2 7.5 13.0 b2 36.2 78.4 8.9 33.9 7.2 1.5 6.4 1.0 5.4 1.0 3.1 0.47 2.8 0.39 187

50.25 15.06 6.73 0.20 2.21 1.20 0.83 2.50 0.70 0.24 70 19.0 99.0 400 174 99 11.2 50 100 18 20 50 9.0 60 26 17 15.0 1.7 25.0 71 2.6 b5 13.5 10.6 12.0 b2 34.7 75.8 8.7 32.8 6.7 1.3 6.0 0.9 5.0 0.9 2.8 0.40 2.4 0.34 179

45.75 16.81 8.15 0.19 2.41 0.80 1.31 2.44 0.65 0.32 73 20.7 99.6 376 185 61 13.2 50 115 24 20 60 13.0 80 30 22 14.0 1.6 28.0 71 2.9 b5 15.8 13.5 14.0 b2 40.1 92.6 10.2 38.7 8.1 1.6 7.1 1.1 5.8 1.1 3.2 0.45 2.7 0.40 213

CRE

387 101 3.4 61

1.1 483 8.4 10.6 2.9 13.1 38.6 76.9 39.2 6.3 1.5 0.8

2.7 0.40

MIO 55.99 13.74 5.17 0.31 2.35 6.28 2.35 3.21 0.70 0.20 62 9.4 99.7 806 138 344 12.9 46 106 21 32 28 3.0 84 19 5 13.3 1.1 35.9 197 5.5 21 12.2 7.7 13.1 0.8 36.1 77.6 8.4 31.4 6.4 1.3 5.3 0.9 5.0 1.0 2.9 0.44 2.7 0.39 180

ACH 71.13 14.36 1.72 0.05 0.36 0.97 3.46 5.02 0.23 0.24 52 1.41 98.95 186 410 82 4.9⁎ b20 22 3⁎ b20 39.4⁎ 20.6⁎ 21.7⁎ b5 37 27 164 4.5⁎ 29⁎ 32⁎ 3–38 3⁎ b2 20 44 25

UCC 66.00 15.20 4.50 0.08 2.20 4.20 3.90 3.40 0.50 0.16 50

550 112 350 4.6 83 60 17 44 25 2.0 71 17 2 12.0 1.0 22.0 190 5.8 17 10.7 2.8 13.2 1.5 30.0 64.0 7.1 26.0 4.5 0.9 3.8 0.6 3.5 0.8 2.3 0.33 2.2 0.32 146

PAAS 62.80 18.90 6.50 0.11 2.20 1.30 1.20 3.70 1.00 0.16 69 6.0 650 160 200 15.0 110 150 23 55 50 2.7 85 20 19.0 27.0 210 5 20 14.6 3.1 16.0 1.0 38.0 80.0 8.9 32.0 5.6 1.1 4.7 0.8 4.4 1.0 2.9 0.40 2.8 0.43 183

For comparison average values are shown for Cretaceous (CRE, Piovano et al., 1999) and Miocene (MIO, Bertolino pers. com.) sedimentary rocks, the Achala (ACH) Batholith (Rapela, 1982; ⁎Pasquini et al., 2004) and PAAS after Taylor and McLennan (1985). Abbreviation normalisation of REE to chondrites after Taylor and McLennan (1985).

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The general weathering trend is directed towards the process of illitization (Fig. 6b; after Fedo et al., 1995). Illite and other illitic minerals (I/S) are the dominant clay minerals detected in both lakes. Fig. 6b shows clearly that the Achala granite is today chemically weathered. Following a typical weathering trend line (after Nesbitt and Young, 1982; Nesbitt, 2003), parallel to the CN-A line would not match the results reported here. One possibility could be the mixing with another source with a different weathering profile, or a secondary chemical weathering after erosion during transport. Commonly, first the Na-rich phases weather towards the K apex, once these phases are converted, the K-rich phases alter into a rather Al-rich composition, assigned by the 90° turn (after Nesbitt, 2003). The ratio Th/U is plotted vs. Th in Fig. 6c and shows a different situation. U is expected to be depleted in weathered samples due to reworking and thus oxidation or during chemical weathering (McLennan et al., 1993). Th concentrations are similar to those in UCC; U is extremely enriched (up to 5 times UCC; see Table 1).

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Thus, the sample plots are far from a predicted weathering trend and display a disturbed signature, unusual for clastic materials. 4.2.3. Trace element geochemistry Comparing both sediments, LM samples are slightly depleted in several trace elements, like Nb, Ta, V, Rb Th and U in relation to SR samples. In other elements (Co, Ni and W) a slight enrichment can be observed. However, more significant are the differences of both sample sets compared to the PAAS set. Only Ga, U and W, besides the REE are systematically enriched. As is also strongly enriched, which largely exceeds the UCC value, but no data for the PAAS exist (see Table 1). Other trace elements, like Rb, Cs, Co, Cu, Th, Sc, Mo, Zn (except the enriched sample LM6) and Y are scattering around the PAAS value (Table 1). Partly, the finer clastic fraction (b2 μm) shows a trend to trace elements concentrations higher than the coarser ones but exceptions can be observed in Sr, Ba, Zr and Nb. Interestingly, As is slightly enriched in the samples

Fig. 6. a) CIA (after Nesbitt and Young, 1982) vs. K/Cs ratio as indicator of increased chemical weathering. b) A-CN-K diagram to demonstrate a possible weathering trend. Along the A-CN apex line the proposed ideal weathering trend of an average igneous source (after Fedo et al., 1995; Nesbitt, 2003; average shale after Taylor and McLennan, et al., 1985). The grey weathering path will represent a simple chemical weathering from the proposed source towards the samples. The stippled line would mark a normal chemical weathering line. c) Th/U vs. Th should demonstrate the weathering in an oxidising climate, thus during transport.

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Table 2 Element ratios LM6

LM6 b 2

Los Molinos Ce/Ce⁎ Eu/Eu⁎ LaN/YbN K/Cs Th/U Nb/Y Zr/Ti Cr/Th Sc/Th Cr/V Y/Ni Zr/Sc Th/Sc La/Sc Ti/Zr U/Th La/Th

1.02 0.70 8.42 1542 1.89 0.50 0.02 4.72 1.04 0.52 0.80 8.18 0.96 2.72 44.63 0.53 2.82

SR5

SR5 b 2

CRE

MIO

ACH

UCC

PAAS

8504 1.6 1.37 0.12 0.63 0.09 0.91 1.35 54.67 10.73 6.67 8.41 0.62 0.62

1.02 0.65 9.2 6100 3.82 0.55 0.06 7.76 1.23 1.38 0.50 14.39 0.81 2.27 15.78 0.26 2.80

1.02 0.66 9.2 2050 4.70 0.70 0.04 7.53 1.10 0.73 0.49 13.13 0.91 2.40 28.55 0.21 2.60

San Roque 1.03 0.67 8.74 1496 1.49 0.37 0.02 4.46 1.16 0.48 1.35 4.92 0.86 2.78 58.08 0.67 3.23

1.03 0.62 9.77 1890 1.27 0.60 0.02 3.70 0.89 0.50 1.25 5.92 1.13 2.89 59.44 0.79 2.57

1.09 0.62 10.04 1534 1.17 0.50 0.02 3.16 0.89 0.43 1.40 5.07 1.13 2.86 54.88 0.85 2.54

towards values over the recommended concentration in soils for residential areas of b 20 ppm (Model Toxics Control Act, Canada). The compositional trend of sedimentary rocks can be estimated by considering the ratios of the highly immobile elements Zr/Ti vs. Nb/Y (after Winchester and Floyd, 1977), recently used for clastic sediments (e.g. Fralick, 2003). The samples in this study point to a mainly andesitic composition, partly caused by the relative depletion of Zr in relation to PAAS, which lowers consequently the Zr/Ti ratio (Table 2). However, low Nb concentrations shift the Nb/Y ratio to a less alkaline composition. Trace elements like Cr are useful to identify accessory basic detrital components like chromite, commonly derived from basic to ultra-basic sources including ophiolites, not readily recognised by petrography or XRD analysis alone. The average Cr content of the UCC is 83 ppm (McLennan, 2001) and in PAAS 110 ppm (Taylor and McLennan, 1985). Basic source terranes would have high ferromagnesian mineral abundances, resulting in high Cr/V ratios (N8) and low Y/Ni (b 0.5). In this case, the ratios of Cr/Th and Sc/Th point to a composition of the detrital material between typical UCC and a felsic volcanic arc (after Floyd and Leveridge, 1987), Cr/V and Y/Ni ratios show clearly that no significant basic input affected the whole sediment composition as their ratios are wide below the above cited ones (Table 2). The REE concentrations normalised to chondrite – here not shown – display a pattern similar to the PAAS.

0.95 0.88

3.66

5.75 1.24

36.87 0.81 2.97 0.27 3.67

0.95 0.63 9.04 2066 1.57 0.37 0.05 3.77 1.07 0.43 1.11 15.06 0.93 2.76 21.24 0.64 2.97

The sums are as well comparable, only SR5 is enriched in REE (Table 1). In comparison to the PAAS (Fig. 7) the LREE (light REE) and HREE (heavy REE) are in three samples slightly depleted, while enriched in sample SR5. However, all samples are enriched in MREE (middle REE) especially in Sm, Eu, Gd and Tb. Other important REE ratios like CeN/Ce⁎, EuN/Eu⁎ and LaN/ YbN (N: chondritic normalised value; Ce⁎ calculation is based on the relation between La and Pr, Eu⁎ is calculated after Taylor and McLennan, 1985) are comparable to PAAS (Table 2). Interestingly, the samples from SR are more enriched in LREE than the samples from LM thus, showing higher LaN/YbN ratios (Table 2). Another trace element, which is concentrated in alarming amounts, is As. It has a relative high residence time in water (Taylor and McLennan, 1985), thus, will be well mixed after a short time, comparable to U, and evenly distributed in all water and sediment systems. The concentrations of As in the sediment are up to 15

Fig. 7. Rare earth element concentrations normalised to PAAS (after Taylor and McLennan, 1985).

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times higher than in UCC (Table 1), and much higher than in healthy water (b10 ppb) and soils of residential areas (recommended value b 20 ppm). Arsenic is controlled mostly by pH values and can differ in a river system or lake. Thus only a larger and thorough study can reveal the exact concentration (e.g. Linge and Oldham, 2002). The general problem of high As concentration is widely known for the whole Chaco– Pampean plains of Argentina (Nicolli et al., 1985; Hopenhayn, 2006).

Sr, Zr, Hf and Pb. This may be explained by sorting effects and probably source composition. REE are mostly PAAS-like, but enrichment in MREE could be observed. Heavy minerals which elevate MREE are partly titanite, rutile and amphibole. Rutile and titanite are as well enriched in Ti and Ca respectively, but both elements are depleted in our sample set. Amphiboles on the other side, were detected by XRD (Figs. 2 and 3) in significant concentration, and can be responsible for such enrichment.

4.2.4. Implications of the major and trace element geochemistry The samples are enriched in Fe, Mn and P, the latter most probably due to the high organic content. Although Fe and Mn concentrations are slightly enhanced, only low to very low concentrations of Fe-oxides or Mnoxides could be detected by petrographic means or via XRD analyses. Nevertheless, the samples are mainly depleted in major elements, which can be interpreted as primarily controlled by detrital sources, rather than environmental conditions. The variable concentrations of Na could be of anthropogenic origin. However, such an interpretation is hypothetical as further geochemical studies would be necessary. Weathering and alteration quantification indices like the CIA and K/Cs ratios point to a strong chemical weathering of the detrital material. Compared with the probable main source, the Achala granite, the sediments are strongly chemically weathered since only physical weathering would not change the mineralogical composition (Nesbitt, 2003). This is in strong contrast to the low Th/U ratios (b3). However, as Th is highly immobile (e.g. McLennan et al., 1990) and unlikely to be added by fluid flow in this setting, the high concentration of U is controlled by detrital influence and does not reflect a weathering profile. W, depleted in upper crustal rocks, as it is a compatible element, is enriched in all samples. The general absence of a significant basic source of sediments, with enriched Cr, Ni and Sc concentrations was demonstrated in the analysis of trace elements. All these elements are less concentrated than in UCC or less abundant than in PAAS. Thus, W does not reflect a basic source, rather a local anomaly caused by a mineralisation (Pampa de Oláen W district) or anthropogenic contamination. Other trace elements are depleted and display as well a lower abundance than PAAS, an unusual trend for fine-grained sediments (Taylor and McLennan, 1985). Normally, shales accumulate trace elements, based on their higher reactivity. In this study, some trace elements are depleted not only regarding PAAS, but also in relation to UCC like Ni, Ba,

4.2.5. Provenance Trace elements like the high field strength elements Th, Sc and Zr and REE are particularly useful for provenance analysis as they are insoluble and usually immobile under surface conditions. Due to their typical behaviour during fractional crystallisation, weathering and recycling, they preserve characteristics of the source rocks in the sedimentary record (e.g. Taylor and McLennan, 1985; McLennan et al., 1993, 2003). A good tracer of basic or less fractionated source components is the compatible element Sc, particularly when compared with Th, which is incompatible and thus enriched in felsic rocks. Both elements are generally immobile under surface, thus, the Th/Sc ratio is considered a robust provenance indicator (Taylor and McLennan, 1985; McLennan et al., 1990). The data of all samples are clustered (Fig. 8a), whereas those from SR show higher Th/Sc ratios (N 1) than those from LM (b 1; Table 2). This composition suggests a tendency towards a volcanic arc. However, continental volcanic arcs and continental crust display relatively similar compositions in some cases (Bock et al., 2000). The Zr concentration in all samples is more than 50% lower than in PAAS or UCC (Table 1). More sensitive elements like Hf plotted against La/Th (Fig. 8b), points to a typical acidic arc composition (after Floyd and Leveridge, 1987). In Fig. 8c the relations between La, Th and Sc are plotted and thus, element concentrations to a larger degree influenced by sorting like Ti and Zr are avoided. Here, the samples lie in the continental arc field. This trend is similar to Cenozoic sedimentary rocks of the Saguión Formation, where a volcanic arc component in some members could be detected (Bertolino and Zimmermann, 2006). For comparison, the data of these young sedimentary rocks are also shown in Fig. 8a–c. Based on this preliminary data set it seems likely to estimate that relatively similar source terranes are responsible for the detrital composition of these two different deposits. Comparing the absolute element composition or element ratios of the sediments with the proposed main source (Achala granite; Table 1) clearly shows the sorting

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Fig. 8. a) Th/Sc vs. Zr/Sc diagram (after McLennan et al., 1990) to reveal the main source composition. b) Provenance discriminating diagram (after Floyd and Leveridge, 1987) shows a derivation for the detrital material from a mainly felsic arc source. Data for the Miocene Saguión Formation from Bertolino and Zimmermann (2006) for comparisons. c) Samples show a strong trend to an arc source, comparable to some samples of the Miocene Saguión Formation (after Bhatia and Crook, 1986).

effect and the mixing with a second source. Sc, Co and V concentrations in the granite are extremely low, but higher in the Cretaceous, Miocene and recent sediments. In contrast, Th and Zr, incompatible elements are higher concentrated in the granite. Thus, a less fractionated source was mixed with the granitic material to form these sediments. However, W is a strong compatible element, which is more largely concentrated in these sediments than in basic rocks and is partly as enriched as in these sediments in ultra-basic rocks elsewhere. U on the other hand is an incompatible element and will be oxidised during transportation and depleted in the sedimentary record (McLennan et al., 1993). Concentrations of U are comparable to the Achala granite, which is as well highly enriched in U regarding UCC (Table 2). As shown, a significant sorting by transport took place to deplete elements like Zr. Thus the slight U loss (see Table 1) cannot be explained by reworking because the concentration should be much lower but arises from a second source highly enriched in U.

4.2.6. Estimates of the environmental conditions using geochemical data Certain elements and element ratios are sensitive of either oxic or anoxic environment as they react differently under these conditions. Trace metals like V, Mn, Cr, Zn, U and Mo as well as Cd can be used to trace an anoxic environment in which these elements are enriched; however Mn can be enriched under oxic conditions as well (e.g. Calvert and Pedersen, 1993; Piper, 1994; Crusius and Sage, 1996; Morford et al., 2001). U is relatively unstable under oxidising conditions but much more stable in anoxic environments, as mentioned previously (McLennan et al., 1993). In our preliminary data U is strongly enriched and the samples are depleted in Zr as a result of sorting. Major element concentrations show that the sediments are strongly weathered. Thus, the abnormal high U may either reflect a specific enriched source or highly anoxic conditions. Bertolino and Zimmermann (2006) demonstrate for Miocene rocks, from northwest Córdoba, that

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high U concentrations coincided with other trace metal enrichment and with facies interpretations towards an anoxic environment. Hence, high U/Th, Mo, V, Cr, partly Cu and Zn as well as Cd concentrations should likely be enriched under anoxic conditions and coincide with CeN/Ce⁎ anomalies lower than 1, interpreted as related to an anoxic environment (e.g. Calvert and Pedersen, 1993; Wilde et al., 1996; Pattan et al., 2005). None of the mentioned elements or element ratios display remarkable values to decipher such an anoxic environment. The slight enrichment in Mn tends to a rather oxic environment (Calvert and Pedersen, 1993). On the other hand, U/Th ratios reach partly the defined threshold ratio of 0.75 (Jones and Manning, 1994) towards an anoxic environment (0.53–0.85; Table 2). Thus, the high U concentrations are not controlled by environmental conditions but inherited from the source (s) like the U mines from the Achala and Cosquín areas, as shown by the mineralogy of SR3 and CB. 5. Discussion The bulk mineralogy of the lake sediments reflects a mixing of different source lithologies exposed within the basin, and is best observed in the rivers' mouths samples. This is well exemplified in the SR lake, where sample SR3 from the mouth of the Cosquín river contains tyuyamunite, taken from the close Mina Rodolfo area (Fig. 1). In the LM lake, the middle catchment area drains mostly over metamorphic rock, which provides oligoclase, garnet, hornblende and eventually cordierite. The influence of granitic rocks is clearly reflected in the clay fraction by kaolinite, the less abundant of opal-C and Fe, Al (hydr)oxides. Sediments from both lakes are fed mainly by UCC material of felsic compositions. Probably, an andesitic or felsic arc related source shed additional material. The samples show, similar to those of Miocene age, a tendency towards a continental arc composition. Since some of the magmatic bodies exposed in the vicinity of the deposits are tentatively related to Cambrian volcanic arc activity (Rapela et al., 1998), this interpretation is a probable scenario for the provenance of the detrital material. However, W as a compatible element does not reflect a basic source but a local anomaly produced by mineralisation. W mineralisation is reported in Pampa de Oláen (Gamba, 1999) and W can easily be eroded into the lake sediments discussed here. The presence of U can be explained similarly. Low Th/U points to unweathered samples and high U/Th ratios to an anoxic depositional environment where U can be enriched. This stays diametral to the general chemical weathering of

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the sediments, shown by low K/Cs ratios and high a CIA (Fig. 6a–b). No trace metal is enriched to reflect anoxic environmental conditions. The occurrence of U–V minerals in the mouth of the river Cosquín supports our interpretation. Additionally, shallow water depths (ca. 35 m) of the lakes do not favour anoxic conditions. The occurring high amount of organic material represents the normal flux of organic matter in this lake system and the oxygen depletion in deep water is recent. This can be recognised by the high activity of bacteria and the growing of cyanobacterias, blue and green algaes. Hence, U is controlled by detrital material, it cannot evaluate weathering trends. Exposed U-rich veins and beds, the granitic body itself, mine dumps or open mine pits and leaching pads contamination would enrich the water or sediments dramatically and enhance U uptake by plants significantly (Chen et al., 2005; Thiry et al., 2005). The most serious concern about the presented geochemical data is that the study concentrates on sediments deposited in an oxic environment, thus enrichment of U cannot take place in these sediments, but the concentrations are extremely high. This implies an enormous loss of U, leached out and stored in “U-traps”, like sediments deposit under anoxic conditions (not likely to have occurred) or by the uptake of plants or organisms. As demonstrated, here analysed sediments are relatively depleted in trace metals, normally concentrated in clays. Elsewhere in the drainage system, clay-rich sediments should occur with enriched concentrations of trace metals and U with extreme concentrations to balance the original content of mineralised sources. In any case, illite, I/S (the main constituents of the clay fraction at SR and LM) and Fe and Al (hydr)oxides, usually present as grains and flake coatings, have been reported as retaining U (Jové Colón et al., 2006) and other metals. SR and LM sediments have been and still are being considered as a possible source of nutrients (N, P) for poor soils (Dirección de Geología, Promoción e Industrias Mineras, Internal Report 1984). If these sediments are used as additives to improve soil fertility, those metals could easily enter the food chain (Amaral et al., 2005; Chen et al., 2005) and become a potential hazard to the population's health. Further investigations will be necessary to establish the extent to which these elements could be released to the water, plants and organisms. This study shows clearly that a comprehensive sampling study has to be conducted to discover contaminated material and prevent massive health problems. The fact that the sediments display different sources of contamination in alarming degrees was shown for U

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and W. The study on Miocene sedimentary rocks has shown that a high concentration of trace metals exists if the environmental conditions are in favour of such enrichment under anoxic conditions (Bertolino and Zimmermann, 2006). The trace metals are mainly compatible elements, like W, but the overall provenance of the detrital material, excludes the significant influence of basic sources categorically. Thus, the source of these element concentrations is only controlled by mineralisation. This is the case for U and W, as U and W are or were mined in closest vicinity (Fig. 1). We report abnormal high concentrations of As, 15 times higher than in UCC (Table 1). It is debatable if in any case the source of As is natural. Long-term exposure to low concentrations of dissolved As causes massive human health problems as reported in West Bengal and Bangladesh (Vaughan, 2006). To evaluate the water, sediments and flora for human consumption, a study has to concentrate on probable traps for such trace metals, like sediments deposited under anoxic conditions with different grain sizes, as some trace metals could have been stored in coarser clastics or heavy minerals. Sorting explains best the relatively scarcity of trace elements, which usually are enriched in normal shales, like Ti, V, Cr and Zr (see Table 1). Thus, only an integrated study would discover the storage sediments, rocks and organic agents for U, W, As and associated trace metals. 6. Conclusions A preliminary study on geochemical characteristics of two sediment fractions from two lakes revealed a granitic composition (typical the UCC sample) for the detrital material. The sediments are highly chemically weathered as reflected by the low K/Cs ratios and high CIA values. They are deposited under oxidising conditions, derived from the distribution of trace metals and Ce/Ce⁎ values, although oxygen depletion in the water has been recently noticed due to eutrophication processes, but this started after deposition and did so far not affect the chemical composition of the sediments. This coincides with the observable facies conditions. The high concentrations of U, W and As are thus only explicable by local anomalies caused by the exhumation of mineralised rocks and mining activity. This can be clearly shown for the lake SR, which is fed by waters derived from abandoned mine dumps or mineralised areas. However, the discussed sediments are extremely unfavourable traps for such contamination, as U is highly soluble under oxidising conditions. Thus, the high concentration is extremely alarming, as other elements

traps (anoxic sediments or flora) have then to balance the contamination and are consequently extremely enriched in U. This can have serious local ecological consequences. W enrichment can be explained by mining activity and mineralised source rocks. The high As concentration is preliminarily related to the mining activity. As in the reported concentrations can cause massive health problems. Finally, this study shows that simple, quick and cheap mineralogical methods combined with geochemical analyses of clay-rich sediments can pinpoint problematic ecological situations. Our study on selected lake sediments reports alarming concentrations of several hazardous trace elements, as the deposits studied here are unlikely preferred storage sites for such trace elements. Thus, until a comprehensive study is conducted, any use of the water, flora and the soil for human or agricultural activity is not recommended, as high contamination cannot be excluded and may enter easily in the human food chain causing severe health problems. We recommend, for comparable studies, to conduct a short interdisciplinary mineralogical and geochemical study interpreted regarding facies constraints and to understand the trace metal concentration in terms of environmental and health constraints. Acknowledgments The financial support was provided by the Secretaria de Ciencia y Tecnología of the Universidad Nacional de Córdoba and the Agencia Córdoba Ciencia S.E. The authors are grateful to Ing. Claudia Oroná for her help on sampling collection and to the Editor, Dr. G. Lagaly for his kind suggestions.

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