Introduction

Lithium (Li) has become a critical metal due to its technological applications, mainly as an essential component in batteries. Currently, lithium is being increasingly extracted from brine-type deposits, but Li-rich pegmatites are still major producers of this element worldwide. In South America, brine-based operations are developed in salt flats located in Chile, Argentina, and Bolivia in what is colloquially known as the “lithium triangle” (Chordia et al. 2022). Pegmatite deposits represent the main Li operations in Australia and China, as well as in other parts of the world (Kesler et al. 2012). Therefore, these bodies have attracted renewed attention as a source of this valuable commodity. In addition to Li, pegmatites concentrate an array of other elements, some of them considered co-products of the exploitation, such as Be, while some others are undesirable toxic by-products, such as heavy metals (Garret 2004). Industrial minerals such as albite, quartz, micas, and potassic feldspar are also exploited from pegmatites. Ores often concentrate in different pegmatite zones, which are defined by specific mineral assemblages, textures and modal proportions (London 2008).

Due to their variable grain size (with individual crystals reaching several meters long) and heterogeneous mineral distribution, it is extremely difficult to calculate the bulk composition of a pegmatite. Nevertheless, some exceptionally well-documented mining operations have allowed an approximation (Simmons et al. 2016). The results show that the overall composition is not substantially different from that of a granite, despite the extremely high local concentrations of some elements such as Cs (in pollucite) or Li (in elbaite, spodumene, and other Li minerals). In some cases, the concentration of some elements apparently enriched (e.g., REE) is even lower than in the parent granite, as it was documented in a pegmatite near Wellington Lake, Colorado, USA (Raschke et al. 2021). Owing to the fact that most mineral components of pegmatites are stable at Earth surface conditions, the release of their components during mineral–water interaction is limited, particularly in regions with weathering-limited denudation regimes such as the one prevailing in Sierras Pampeanas of Córdoba (Campodonico et al. 2014). The incongruent alteration of aluminosilicates results in the formation of secondary minerals such as clays or Fe/Mn/Al (hydr)oxides, and the release of solutes, mainly alkaline and earth-alkaline ions, bicarbonate and H4SiO4. Trace elements, or elements that are essential structural components in some pegmatitic minerals (e.g., U, Li, Bi, Nb, Ta, Sn, REE), are also released and impart their geochemical signature to nearby soils, sediments, and waters. This has at least two implications. On the one hand, elevated concentrations of some elements that are released along with Li may be harmful for living organisms, particularly in soils and water reservoirs (e.g., Nguyen et al. 2021). On the other hand, anomalous concentrations of Li and associated elements that extend outwards from buried pegmatites could serve as pathfinders of hidden mineralized bodies (e.g., Galeschuk and Vanstone 2005).

The increasing world demand of Li has sparked interest in the deposits of the Pampean pegmatite Province, located in central Argentina (Galliski et al. 2022). Las Tapias pegmatite, located in western Córdoba Province (Central Argentina), has been mined for beryl (Al2Be3Si6O18), spodumene (LiAlSi2O6), bismuth-bearing minerals and industrial materials (quartz, feldspars). More than 1110 tons of spodumene, about 8 tons of Bi minerals, and more than 2400 tons of beryl have been extracted since 1939 (Angelelli 1984). The operation is located near a small village (also named Las Tapias, Fig. 1), in a valley where the main economic activity is tourism. For such reasons, the inhabitants are concerned about the environmental impact that a potential expansion of the mine's activities would cause, mainly in the water quality of the main local rivers, which are the source of drinking water in the area.

Fig. 1
figure 1

Location of the study area showing the Los Sauces River basin and the Panaholma (A), Mina Clavero (B), and Las Tapias sub-basins (C)

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Lithium is a metal that is used for treatment of a number of medical disorders (both physical and psychological), most notably bipolar disorders. The medical dose is best kept under 1.0 mmol L−1 (equal to ~ 70 µg L−1 Li), as higher doses could be associated with toxicity and increased side-effects (Barroilhet and Ghaemi 2020). This same value has been suggested by the United States Geological Survey, assuming that the only Li source is drinking water (i.e., disregarding Li intake due to food consumption such as dairy products and eggs). However, it should be stressed that at present, there is no regulation setting an upper limit in Li concentration in drinking water, neither in the USA (Lindsey et al. 2021) nor in Argentina (CAA 2012).

The present work aims to assess the impact of mining activities of a Li-rich pegmatite carried out in Las Tapias deposit, on the chemical composition of the basin’s stream that drains the region, and to evaluate whether the chemical signature of local waters can serve as an environmental indicator related to the presence of Li pegmatite deposits. To achieve this goal, water samples of Las Tapias stream drainage basin were collected upstream and downstream the mine, and their major and trace element chemical composition was analyzed in order to characterize spatial trends and to identify anomalies compared to the background chemical composition of stream waters in nearby basins.

Study area

Las Tapias stream drainage basin is a typical mountain hydrological system flowing along the western slope of the Sierras de Comechingones, Córdoba province, central Argentina. The Sierra de Comechingones is one of the southernmost ranges of the Sierras Pampeanas in central Argentina, which consist of Palaeozoic basement blocks bounded by faults (González Bonorino 1950) and uplifted as a result of Cenozoic Andean compression (Isacks 1988; Jordan and Allmendinger 1986). The Sierra de Comechingones is mainly composed of Early Cambrian middle- to high-grade metamorphic rocks and Cambrian to Devonian granites (e.g., Rapela et al. 1998, 2008; Dahlquist et al. 2014). These basement rocks are unconformably overlain by unconsolidated Early Cenozoic sediments (e.g., Bonalumi et al. 1998).

Las Tapias stream catchment is part of the Los Sauces River basin (Fig. 1), one of the systems that drain the northwest portion of Córdoba province (Dasso et al. 2014). The Los Sauces River rises from the confluence of the Mina Clavero (catchment area of about 200 km2) and Panaholma (catchment area of about 325 km2) rivers. About 20 km downstream, this confluence receives the waters of Chico de Nono River and finally, flows into the La Viña reservoir (Fig. 1). Most of Los Sauces hydrological basin runs over Achala Batholith’s granites (mostly porphyritic or equigranular monzogranite), and the Early Cambrian basement metamorphic rocks consisting of amphibolite and granulite-facies metapelitic rocks, with scarce amphibolites and marbles (Fig. 2). Las Tapias stream catchment occupies an area of about 150 km2, being Los Hornillos (18.8 km-long), Las Chacras (12.9 km-long) and Los Molles (15.8 km-long) its main tributaries. After their confluence, the 8.9-km-long Las Tapias stream flows from E to W and discharges into the Los Sauces River, a few kilometers downstream La Viña reservoir, near Villa Dolores city (Fig. 2).

Fig. 2
figure 2

The Las Tapias stream catchment, including the outcropping rocks and the location of Las Tapias mine. Water sampling points are indicated

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The climate in the region is mesothermal semi-arid, with a mean annual temperature of 18 °C, the average minimum is 5 °C, and the maximum 32 °C (1981–2010 record period, Villa Dolores gauging station, www.smn.gob.ar). Most rainfall occurs during the austral spring and summer, i.e., October to March (> 35 mm/month for the same record period), with dry winters (< 35 mm/month). The mean annual rainfall is 648 mm. During the warm months, evaporation exceeds precipitation, thus resulting in a negative water balance. The climatic and landscape features of the study area determine a “weathering-limited” regime in the sense of Carson and Kirkby (1972). It means that transport processes are more rapid than chemical weathering, and therefore, a significant part of the regolith is rapidly removed by physical processes.

Several pegmatites corresponding to the Altautina District (Galliski 1999), and collectively known as Las Tapias deposit, crop out in the basin. They are located near the homonymous village in San Javier department (Fig. 1, 31° 56′ 29.02″ S, 65° 05′ 13.66″ W). Las Tapias village has a stable population of 1936 inhabitants (INDEC 2010) that increases markedly during the austral summer due to tourism.

The Las Tapias pegmatite belongs to the LCT petrogenetic family and is of Rare Earth Elements (REE) class, REE-Li subclass, complex type, spodumene subtype, following the classification of Černý and Ercit (2005). Linares (1959) established an age of 520 ± 25 Ma (U–Pb in uraninite) for the pegmatite, which indicates that it was formed during the Pampean orogeny. The host rocks are known as the Altautina Schists and belong to the Guasapampa Metamorphic Complex. The Altautina Schists comprise biotite-quartz schists and mica-schists, with scarce marble and calc-silicate lenses. The schists are mainly composed of quartz-plagioclase-biotite-muscovite-tourmaline- magnetite, in different modal percentages. Locally, these minerals may define light (quartz-rich) and dark (biotite-rich) bands. These rocks are intruded by thin tonalite dikes and are crisscrossed by quartz veinlets.

The main body of the Las Tapias pegmatite, which is the most important for its volume and mineral production, is intruded in a lens of hornblendite that occurs as two textural varieties (porphyritic and equigranular). Black amphibole (identified as tschermakite by Porta et al. (1994), but currently classified as ferro-hornblende according to the scheme of Hawthorne et al. 2012) is the main rock-forming mineral, associated with plagioclase, quartz, titanite and biotite; chlorite, epidote and iron oxides occur as secondary phases.

Las Tapias is a tabular body at least 100 m long and up to 12 m thick that strikes approximately E–W and dips 18°–30° S. Galliski (1999) described an asymmetric vertical zoning which, from the upper contact downwards, is defined by:

  1. 1.

    Border zone: muscovite in a matrix of K-feldspar and quartz (± black tourmaline and biotite).

  2. 2.

    Monomineralic zone: composed of quartz.

  3. 3.

    Outer intermediate zone: blocky K-feldspar with minor quartz and albite; accessory phases are spessartine, beryl and altered spodumene.

  4. 4.

    Intermediate zone: quartz with albite, and filling units composed of muscovite.

  5. 5.

    In the contact between zones 3 and 4, in the quarry center: there is a discontinuous zone made of quartz + albite but with major amounts of beryl.

  6. 6.

    Lower intermediate zone: made of quartz and microcline with large (meter-sized) crystals of spodumene, with muscovite, spessartine, chalcopyrite, beryl, and minor accessory phases.

The lower contact is not exposed, so there are probably other zones present as well. Spodumene is present in an intermediate zone, composed mainly of quartz (~ 80–85% vol.) and spodumene (~ 10–15% vol.), with small amounts of plagioclase, microcline and muscovite. Spodumene occurs as tabular prismatic crystals embedded in quartz, up to 2 m long (but usually closer to 1 m), and of grayish green color (Fig. 3). Some penetration (Angelelli 1984) and lamellar twins were observed. Unlike spodumene from other Argentine localities, this pyroxene from Las Tapias contains a non-negligible amount of Fe, up to 2.72 wt% Fe2O3, as well as Mn (up to 0.51 wt% MnO); both of them replace Al. The only other element consistently present is Na (up to 0.18 wt% Na2O), replacing Li. Alteration to fine-grained muscovite or a mixture of albite + muscovite is common in some parts of the pegmatite.

Fig. 3
figure 3

a General view of the main quarry of Las Tapias pegmatite. The white arrow marks the contact between the hornblendite (upper mafic rock) and the pegmatite. Bulldozer for scale. b Tabular crystals of fresh spodumene

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Beryl occurs as anhedral masses and prismatic crystals up to 80 cm long, ranging from pale blue, greenish to yellow; white and pink beryl occur in the spodumene-bearing zone. Small amounts of Cs were detected by EDS in the pink variety (morganite); although no Li measurements were performed, the ratio of the unit cell parameters (c/a, as indicated by Aurisicchio et al. 1988) suggests that morganite contains some Li (Colombo et al. 2004). Accessory phases present at Las Tapias pegmatite include spessartine, tantalite-Mn, U- and Pb-rich members of the microlite group (Galliski and Černý 2006), uraninite, chalcopyrite, pyrite (usually heavily altered to Fe hydroxides), bismuthinite and its alteration product bismuthite, and traces of magnetite. Other alteration phases present in very small quantities are pucherite, mottramite, calcite, malachite and azurite (Angelelli 1984; Gay et al. 1994; Galliski 1999; Colombo and Lira 2000).

Black tourmaline occurs as thin prismatic crystals scattered in muscovite and plagioclase, but is much more abundant in the host schists close to the contacts, attesting to a strong boron metasomatism produced by fluids exsolved from the pegmatite. Holmquistite, {Li2}{Mg3Al2}(Si8O22)(OH)2, a Li-bearing amphibole, was reported as pale purple radiating masses formed in the contact between the pegmatite and the hornblendite, as ferro-hornblende reacted with Li-bearing solutions exsolved from the pegmatite (Porta et al. 1994).

Materials and methods

Sampling and analytical determinations

Water samples from Las Tapias drainage basin were collected in December 2019. Figure 2 shows the location of the sampling sites, while their geographical coordinates are reported in Table 1. Water samples were taken from tributaries, i.e., LT1, LT2, and LT4, and from the mainstream, i.e., LT5, LT6, and 2LT8. The latter sample was collected after a precipitation event occurred on December 4, 2019. A rainwater sample (LT-LL) of this event was collected manually with a plastic funnel-type collector at ground surface. To avoid dry deposition, the rainwater sampler was deployed as soon as the rain began and retrieved immediately after rain stopped. Additionally, a sample of groundwater from a domestic well (LT-P) was also collected near Las Tapias village.

Table 1 Location, physico-chemical parameters and major dissolved composition of Las Tapias stream drainage basin
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Routine field parameters were measured in situ: pH, electrical conductivity (EC), total dissolved solids (TDS), temperature and alkalinity. These determinations were performed following standardized methods (e.g., Baird et al. 2017). The pH was measured using a portable pH meter. Electrical conductivity (EC), temperature and total dissolved solids (TDS) were measured using a Hach portable conductivity meter. Alkalinity was determined by titration using 1.6 N H2SO4 bromocresol green-methyl red and phenolphthalein as endpoint indicators (Hach Co). Water samples were filtered after collection through 0.22 µm cellulose acetate membrane filters (Millipore Corp.) and divided into two aliquots. The filtration equipment was repeatedly rinsed with sample water prior to filtration. One aliquot (15 ml) was acidified to pH < 2 with ultrapure HNO3 for major cations and trace elements determinations and stored in pre-cleaned polyethylene bottles. The remaining aliquot (100 ml) was stored without acidifying in pre-cleaned bottles, at 4 °C for the determination of major anions.

Anions (Cl−, SO42−, NO3−, NO2− and F−) were determined by ion chromatography with chemical suppression of eluent conductivity (Metrohm 930 Compact FLEX IC), while cations and trace elements were measured by inductively coupled plasma–optical emission spectrometry (ICP–OES, iCap Thermo). For all the analyzed water samples, the charge imbalance between cations and anions was less than 10%.

Enrichment factor

Enrichment factor (EF) represents the extent to which elements are enriched or depleted relative to a selected reference material (Iqbal and Shah 2015). This value is frequently used to identify potential enrichments of metals derived from human activities in natural samples or due to weathering processes. For calculation, the target element is usually normalized to elements that are relatively immobile during rock alteration, such as Al, Mn, Ti, Zr, Sc and Cr. The use of a reference element makes the EF more effective than other indices such as the pollution index (PI) which is just the ratio of the concentration of the element of interest in the sample relative to the background (Chen et al. 2005).

The EF has been widely employed in riverine sediments to assess anthropogenic metal pollution in aquatic ecosystems (e.g., Islam et al. 2015; Selvaggi et al. 2020), as well as in soils; to estimate the impact of anthropogenic activities such as mining and industrial activities (e.g., Almasoud et al. 2015; Bern et al. 2019); to study pedogenetic processes (e.g., da Silva et al. 2020); and to assess contributions of anthropogenic sources on its soluble chemical composition in rainwater (e.g., García et al. 2022). They have also been applied to analyze the mobility and re-distribution of major, trace and rare earth elements through weathering profiles (e.g., Webb and Girty 2016; Campodonico et al. 2019; Fu et al. 2019). In river waters, the studies that employ EF are scarce, and they aim to identify the sources of enrichment/distribution patterns of heavy metals as well as the level of contamination (e.g., Dan et al. 2014).

The EF for each element was calculated as follows:

$${\text{EF}} = [(C_{x} /C_{{{\text{ref}}}} ){\text{sample}}]/[(C_{x} /C_{{{\text{ref}}}} ){\text{background}}]$$
(1)

where the concentration of the element of interest is Cx, and the concentration of a reference element for the purpose of normalization is Cref. In this case, in order to estimate rock weathering contributions and anomalous element concentrations, local rainwater was used as background and Cr was chosen as reference element because its concentration remains almost invariable between local rainwater and stream waters. Local rainwater was selected as the background because it is the main source of water recharge to the study watersheds. The degree of enrichment due to rock weathering was interpreted based on the scale proposed by Birch and Davies (2003):

EF < 1: no enrichment;

1 ≤ EF < 3: minor enrichment;

3 ≤ EF < 5: moderate enrichment;

5 ≤ EF < 10: moderately severe enrichment;

10 ≤ EF < 25: severe enrichment;

25 ≤ EF < 50: very severe enrichment;

EF > 50: extremely severe enrichment.

Results and discussion

Hydrochemistry

Table 1 shows the main hydrochemical parameters measured in situ in Las Tapias stream basin; the collected rainwater and groundwater samples are also included. The analyzed stream waters are neutral to alkaline, with pH varying between 6.75 and 8.55, with a mean value of 7.82. The EC values range between 231 and 574 μS cm−1, while TDS contents range between ~ 115 and ~ 287 mg L−1. According to the TDS concentrations, stream waters are of the non-saline water type (< 1000 mg L−1). No spatial variation was recognized in pH values. Unlike this parameter, EC and TDS values increased downstream. The groundwater sample is neutral (pH 7.4) with EC of 615 μS cm−1 and TDS of 309 mg L−1, whereas rainwater is, as expected, diluted (TDS = 9 mg L−1) and slightly acidic (pH = 6.87). Groundwater highest dissolved concentrations indicate longer water–rock interaction when compared to superficial waters.

The major chemical composition of stream waters, groundwater and rainwater is also reported in Table 1, along with concentrations of minor constituents such as NO3−, NO2− and F−. The corresponding mean concentrations determined in the Mina Clavero and Panaholma rivers (except F−), that belong to the upper Los Sauces hydrological basin, are also reported (Lecomte 2006). These data correspond to sampling carried out in 2003–2004 during the same hydrological period of the year (i.e., November–December). Samples were collected along each basin, from the headwaters to the lower catchments, including tributaries and the mainstreams. Mean values were calculated with 15 samples from Mina Clavero River and 17 samples from Panaholma River.

Major dissolved anions show a relative abundance (in meq L−1) characterized by HCO3− > SO42− > Cl−, whereas the cation relative abundance is Ca2+ ≥ Na+ > Mg2+ > K+. According to their major chemical composition, Las Tapias stream waters are of the mixed-bicarbonate type, with a general trend of increasing SO42− downflow (Fig. 4). The groundwater sample shows the same chemical signature, while the rainwater is of the calcium-sulfate/chloride type. The major chemical composition of stream waters in the Las Tapias basin is encompassed within the fields corresponding to the chemical variability spanned by waters of the Panaholma and Mina Clavero basins (shadowed areas in Fig. 4). Nevertheless, the average concentrations of major ions in the study basin are from 3 to more than 10 times higher than the corresponding values measured in the other tributaries of the Los Sauces basin (Table 1). Likewise, the values of mean EC are more than 6 times higher than the mean values determined in the Mina Clavero and Panaholma rivers (Table 1).

Fig. 4
figure 4

Las Tapias’ water classification according to Piper (1944). Compositional fields of Mina Clavero and Panaholma rivers (Lecomte 2006) are also indicated

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Interestingly, minor ions such as NO3−, and NO2− show mean concentrations that are similar to or even lower than those reported in the upper basin of the Los Sauces River (i.e., Mina Clavero and Panaholma rivers). Nitrites and nitrates, which are typically contributed by anthropic sources, are in very low concentrations in the analyzed stream waters (NO3− < 1.5 mg L−1 and NO2− < 0.09 mg L−1). Moreover, F− concentrations in most stream waters along the Sierras Pampeanas region are the result of the weathering of F-rich micas and F-bearing accessory minerals (García et al. 2012, 2014; Borgnino et al. 2013; Uran et al. 2022) that compose the A-type granites and pegmatites emplaced in the region (i.e., Dahlquist et al. 2010).

The dissolved trace elements reported in Table 2 are essential structural components or impurities in the minerals that compose the Li-rich pegmatite and the dominant lithology in the study basin. As shown in Table 2, the average concentrations of most dissolved trace metals in the Las Tapias basin are remarkably higher than those of the Panaholma and Mina Clavero rivers, thus suggesting contributions from local sources, either natural or anthropogenic.

Table 2 Trace elements dissolved concentrations in Las Tapias stream basin
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Dissolved Li concentrations in the Las Tapias stream range from 31 to 114 μg L−1. These values are from 30 to 100 times higher than the average abundance of dissolved Li in world rivers (1.84 μg L−1, Gaillardet et al. 2011), but markedly lower than the concentrations reported in the Puna-Altiplano brines and river waters, where Li values are usually in the order of thousand mg L−1 (e.g., López Steinmetz et al. 2018; García et al. 2020; Godfrey and Álvarez-Amado 2020). At a basin scale, the Li mean concentration in the Las Tapias stream is ~ 75 μg L−1 which is ~ 6–18 times higher than the corresponding average values determined in the Panaholma and Mina Clavero sub-basins (Table 2).

Besides Li, Table 2 reports the concentrations of heavy metals, such as Zn, Cr, Cu, and Ni, as well as Be, V, Fe, Mn, Sr and Ba. The most concentrated heavy metals in the study stream waters are Sr and Fe, while the lowest detectable concentrations correspond to Cr and Be. Moreover, As, Ag, Co, Cd, Se, Pb, and Mn were determined but not included in Table 2 because their concentrations were below the detection limit of the analytical method (i.e., 2.5, 4, 1.6, 0.3, 15, 6.2, and 0.5 µg L−1, respectively). Despite the longer time of water–sediment interaction in the aquifers than in surface waters, the concentrations of Li and heavy metals measured in the groundwater sample are not statistically higher than the corresponding mean concentrations determined in surface waters.

Sources of solutes in the Las Tapias basin

It is well known that water chemical composition of rivers is mainly controlled by rainfall inputs, differential weathering of silicate and carbonate minerals, and dissolution of evaporitic minerals (e.g., Meybeck 2011). However, the geochemical evolution of waters is also regulated by several processes such as ion exchange, water mixing, adsorption/desorption, nutrient recycle, and atmospheric exchange (e.g., Lecomte et al. 2005; Goldsmith et al. 2010). In addition, in the current context of global change, anthropogenic activities such as mining activities, urban wastes, agriculture, and cattle breeding, are modifying the natural geochemical signature of waters more and more often, even in hydrological systems that were previously considered pristine (e.g., Petelet-Giraud et al. 2009; Pasquini et al. 2012).

Gibbs (1970) proposed that three major mechanisms, i.e., atmospheric precipitation, rock weathering, and evaporation/precipitation processes, control water chemical composition in world rivers. In Fig. 5a, stream water, groundwater and rainfall samples collected from the Las Tapias basin were plotted in the classical Gibbs’ diagram. With the exception of the rainwater sample that, as expected, plots in the atmospheric precipitation field, the remaining surface and groundwater samples plot on the field of rock weathering, indicating that their chemical composition is the result of rock–water interactions. In addition, to identify the relative contribution of the different lithologies to water chemistry, samples were plotted in the diagram of Fig. 5b (modified from Oliva et al. 2004). The plot shows the relationship between Mg/Na and Ca/Na molar ratios in the water samples and includes a field (shadowed area) that defines the chemical signature of rivers draining metamorphic rocks in Sierras Pampeanas (Lecomte et al. 2005; Formica et al. 2015) and specific mineral domains (Oliva et al. 2004). Stream waters from Las Tapias, as well as the other tributaries of Los Sauces River (i.e., Panaholma and Mina Clavero rivers), and the groundwater sample, plot close to the silicate endmember. Besides, Las Tapias waters plot within the field of rivers draining metamorphic domains in Sierras Pampeanas, revealing that the dissolved load is mainly supplied by the weathering of rock-forming minerals that compose the host schists.

Fig. 5
figure 5

a Gibbs’ diagram of Las Tapias stream water samples. Samples of rainwater and groundwater are also included. b Mg/Na vs. Ca/Na diagram modified from Oliva et al. (2004) for Las Tapias stream and the groundwater samples. The other tributaries of Los Sauces River (i.e., Panaholma and Mina Clavero rivers) are also included. The shadowed area represents the chemical composition of rivers draining metamorphic rocks in Sierras Pampeanas

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The formation of mineral deposits involves the concentration and subsequent dispersion of elements of economic interest. When minerals are exposed to the conditions prevailing at, or close to the Earth's surface, these elements are released into the water. Thus, in watersheds overlying mineral deposits, the concentrations of elements of economic interest in water and sediments are anomalous compared to corresponding regional background values. Elemental enrichment in Las Tapia's stream water is most evident in highly mobile trace elements such as Li, Rb, Sr, V, and some heavy metals such as Zn, Cu, and Ni (Table 2).

Previous research (e.g., Trueman and Černý 1982; Galeschuk and Vanstone 2005) has shown that Li gives a strong apical response in rock or soil samples collected directly above the buried pegmatite. However, this geochemical signature falls rapidly to or close to background levels a short distance away from the body. In the case of Las Tapias pegmatite, there are no water courses running directly on or very close to the body. As could be expected, and indeed confirmed by the chemical analyses presented in this contribution, unlike what is observed in stream waters flowing through metamorphic host rocks, the pegmatite influence on the geochemical water signature cannot be detected.

There are no published values of the Li content in the host rocks (neither metamorphic nor igneous) in the study area. However, the high Li content of the schists (inferred from the abundance of Li released by dissolution of these rocks) would make them a fertile lithology for the generation of a Li-rich anatectic melt that eventually gives rise (most probably after differentiation) to lithium-bearing pegmatites. This is the most common origin for these deposits, which are related to S-type granites (e.g., London 2008). In this regard, the whole zone could be an interesting target for the search of hidden pegmatite bodies. The high value of Li detected on the water sample taken above granite (LT1) is enigmatic, as there are no known Li-bearing pegmatites related to this rock. However, this could merely reflect a search bias, or pegmatites may be covered by soil or rock. The bodies known as La Juana pegmatite, located not far from La Tapias mine, are related to the Loma de La Población granite (Varas et al. 1997) and carry Li-bearing minerals such as lepidolite and elbaite (Gay et al. 1990).

To identify potential anomalies due to the impact of Li-rich pegmatite and its host rocks on the stream water chemistry, dissolved elements concentrations determined in the Los Sauces River sub-basins (i.e., Mina Clavero and Panaholma rivers, and Las Tapias stream) were normalized to the mean Upper Continental Crust (UCC) composition (McLennan 2001). The world average river concentrations (Gaillardet et al. 2011; Meybeck 2011) were included for comparison. As seen in the diagram of Fig. 6, the normalized dissolved concentrations in the study basin are from 103 to 107 times lower than the UCC. Most elements from Las Tapias stream represented in the spidergram of Fig. 6 show UCC-normalized concentrations higher than the corresponding ratios determined in the neighbor sub-basins (i.e., Mina Clavero and Panaholma) and in the world rivers average. The only exception is Fe that evidences low dissolved concentrations, probably because it tends to precipitate in the form of (hydr)oxides at the pH values of the studied waters.

Fig. 6
figure 6

Upper Continental Crust (UCC)-normalized multi-elemental diagram of Las Tapias dissolved components. Mean Mina Clavero and Panaholma rivers compositions are also shown. World average rivers major (Meybeck 2011) and trace (Gaillardet et al. 2011) elements composition is included for comparison

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Higher UCC-normalized concentrations observed in the Las Tapias stream waters can be assigned to the weathering of the more labile aluminosilicates that are present in the host rocks. At the magmatic stage, spodumene can typically be altered to a mixture of muscovite + albite or to clay minerals. The first alteration is produced by high-temperature fluids, probably related to the last consolidation stages of the pegmatite, whereas replacement by clays is usually ascribed to meteoric alteration, i.e., by infiltrating fluids, and at much lower pressure and temperature (London and Burt 1982; Angelelli 1984). In either case, most Li is removed during alteration, leaving products that contain this metal in much lower concentrations. The albite + muscovite alteration that replaces spodumene at Las Tapias contains 0.58 wt% Li2O (Angelelli 1984), in contrast to 7.90–8.00 wt% Li2O in fresh spodumene from the same locality. At Las Tapias, spodumene pseudomorphs are composed of fine-grained albite + muscovite, so it can be inferred that the alteration occurred early in the post-magmatic stage (in the Lower Palaeozoic), and that most Li was released to the surrounding host rocks, where it has been later scavenged by holmquistite crystallization produced by metasomatic reactions, or lost.

Natural vs. anthropogenic stream water chemical signature

Enrichment factors were calculated in order to identify the extent of elemental enrichments due to natural or anthropogenic contributions to the water (EF, Table 3). Natural contributions are those related to the weathering of regional rocks and in the study area, are represented by elements such as Li, V, Cr and Ba. The Li EF values reveal an extremely severe enrichment (mean value: 121) for las Tapias stream and Panaholma River (mean value: 71), whereas the Li EF for Mina Clavero is 25 in average, indicating severe enrichment. When analyzing the variability of Li EF in the Las Tapias basin, it is clear that the highest EF is registered at the river´s headwaters, while the downflow trend is variable (Table 3). This behavior suggests important Li contributions from the weathering of the country rocks, especially at the stream’s upper catchment, whereas mining activity does not produce an evident Li enrichment in the stream water downflow the mine.

Table 3 Enrichment factors (EF) of major ions and trace elements in the studied waters
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Micas are labile minerals in the country rocks that may supply Ba, V, Cr, Cu, and Zn (e.g., Tischendorf et al. 2001; Scott and Pain 2009) to the studied stream waters. EFs calculated for these elements in Las Tapias stream indicate a general pattern of minor enrichment for Zn; moderate enrichment for Cu and V, and severe for Ba. On the contrary, the corresponding average EFs calculated for most trace elements in the Mina Clavero and Panaholma rivers show minor or no enrichment (Table 3). On the other side, enrichments in Ca2+, Na+, Mg2+, K+, HCO3− and Sr in streamwater from Las Tapias reflect the weathering of plagioclase, biotite and muscovite. The same behavior was observed in the Mina Clavero and Panaholma rivers.

Particularly noteworthy is the downstream enrichment of major and trace elements between sampling stations LT5 and LT6, where the influence of mining and urban activities is expected to be more evident. Among major ions, increments in SO42− and Cl− concentrations can be almost univocally assigned to urban wastewater contributions. At a sub-basin scale, sulfate EF varies in one order of magnitude from the upper basin to the lower stretch, whereas Cl− EF exhibits a value three times higher in the lower basin compared to that calculated in the upper catchment (Table 3). This is in concordance with the chemical evolution of waters according to Piper’s classification (Fig. 4). However, as mentioned above, this increase downstream would be due to anthropogenic sources. It is widely known that both dissolved components (i.e., SO42− and Cl−) in rivers can increase significantly by anthropogenic pollution (e.g., Meybeck 2011). Figure 7 shows the molar relationship between SO42− and Cl− in Las Tapias stream basin compared with this ratio in local rainwater. The main tributaries show a similar ratio to that of rainwater, while a clear increase is evident downstream. In addition, Fig. 7 also shows a high correlation between both anions (p < 0.001), suggesting a common origin. This reinforces the hypothesis of anthropogenic contributions, probably derived from domestic wastes, considering that the mainstream drains through Las Tapias village, whose population increases during the austral summer (when sampling was carried out) as the result of tourism activity. Furthermore, groundwater reflects the same behavior, since it shows a Cl− vs. SO42− ratio similar to that determined in the stream water of the lower stretch. On the other hand, the water sample taken after the rainfall event (i.e., 2LT-8) clearly evidences a dilution effect (Fig. 7).

Fig. 7
figure 7

Dissolved chloride vs. sulfate in Las Tapias stream basin

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Conclusions

This work analyzes the hydrochemical signature of the Las Tapias stream basin, a small mountain watershed in the Pampean ranges of Córdoba, central Argentina, that drains a region where a Li-rich pegmatite is being mined. Las Tapias stream presents circumneutral to alkaline waters, with TDS varying from 115 to 287 mg L−1. The waters are of the mixed-bicarbonate type, evolving to a more sulfated composition downstream. The major dissolved chemical signature indicates that weathering of the outcropping rocks is the main source of solutes. However, the increase in sulfate concentration downstream, accompanied by a similar behavior of chloride, suggests an anthropogenic source for these anions.

In a regional context, Las Tapias stream basin shows a higher dissolved load concentration than other rivers draining the region (i.e., Mina Clavero and Panaholma rivers), although its area is significantly lower. This is evident in the TDS concentration but particularly in trace elements. Calculated enrichment factors confirm that Li is noticeably enriched (more than two times) compared to these other mountain rivers. Besides, V, Cu, Ni, and Ba also show higher enrichment factors than Mina Clavero and Panaholma rivers, indicating that the weathering of labile phyllosilicates that compose the host rock (i.e., schists) impart high concentrations of these trace elements. Thus, the hydrochemical signature of local waters implies that these rocks are fertile protoliths for S-type granites and derived Li-bearing pegmatites, and that the area could be an interesting regional target for exploration of hidden pegmatites.

Finally, it is evident that the mining activities at the Li-bearing Las Tapias pegmatite have a negligible effect on the hydrochemical signature, and therefore, it does not constitute a source of water pollution in the basin. The obtained results provide valuable information about the environmental implications on surface water in a lithium mineralized area and provide a background value for lithium in Las Tapias basin. Considering local inhabitant concerns about environmental pollution derived from the mine, it is expected that these insights would help the local government authorities to make reasonable decisions toward future activities in Las Tapias mine.

Further work regarding the surrounding sediments geochemical signature is required in order to evaluate the impact of extractive activities on the solid load transported in Las Tapias stream basin.