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Partitioning of minor, trace elements and rare earth elements in bentonite affecting by thermal alteration
Applied Clay Science xxx (xxxx) xxx–xxx
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Research paper
Partitioning of minor, trace elements and rare earth elements in bentonite affecting by thermal alteration E. Caballero⁎, C. Jiménez de Cisneros Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Avda. de las Palmeras, 4, 18100 Armilla, Granada, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords: Minor elements Trace elements Rare earth element Bentonite Cabo de Gata (Almería Spain)
Minor and trace elements, included the rare earth elements (REE), of bentonite that has undergone the natural action of a thermal alteration have been determined. This study has been conducted in the Cala del Tomate outcrop, Cabo de Gata region (Almeria Spain), where an important volcanic dome has intruded in a bentonite mass producing a temperature gradient from the contact area to the exterior. Data are compared with those obtained in bentonites that not were subjected to the thermal effect. No major differences in the REE distribution of bentonite subjected to a thermal contact area in front of a stratigraphic contact zone have been found. On the whole, the contact metamorphism causes element mobilisation, depending on whether there is a temperature gradient. Elements whose behaviour depends directly on temperature, behave as qualitative indicators of element mobility. Rb mobilises significantly near a thermal contact, a pattern that contrasts with its behaviour in a mechanical contact. Other elements that are sensitive to the effect of temperature are lithophile elements. These elements demonstrate a fractionation of Light Elements Lithofile Elements (LILE) compared with High Field Strong Elements (HFSE) near the thermal contact. The main chemical differences with the stratigraphic contact area not subject to the effect of temperature are the incorporation of trace elements with a small radius (HSFE) in the structure of the smectites subject to the effect of temperature, to the detriment of those with a larger radius (LILE).
1. Introduction Several studies show that crystal chemistry exerts a major control on trace element partitioning (Wood and Blundy, 1997, 2001). Marks et al. (2004) compared the trace element contents of mafic minerals in order to investigate the partitioning behaviour of trace elements in natural alkaline silicate melts. Trace elements determination in basaltic systems have been developed by Coogan et al. (2000); Thompson and Malpas (2000); Tiepolo et al. (2002), in hydrothermally altered rocks by Shikazono et al. (2008), in process of alteration of rhyolitic rocks to bentonite by Muchangos (2006) and element mobility during the bentonite formation have been studied by Özdamar et al. (2014). In most minerals, trace elements fill lattice sites by replacing the main element of the lattice. They can be precipitated within cracks of the crystal in special composition. Although the level of trace elements is as low as parts per thousand (ppt), and part per million (ppm) in soil or rocks, they can provide useful metal deposits which can have economical importance. Rare earth elements (REE) in sedimentary rocks concentrate in the silt and clay fractions and their contents appear uncorrelated with clay
⁎
mineralogy (Cullers et al., 1979). The differences in the REE content may be inherited from the REE composition of the source rock or determined by chemical weathering processes in the source area (Banfield and Eggleton, 1989). Generally, the incompatible element composition of bentonites is similar to that of the surrounding volcanic rocks, suggesting that the incompatible elements were generally immobile during alteration processes (Arslan et al., 2010). REE distribution in the clay fraction of sediments from central Portugal was studied by Prudencio et al. (1989) who suggested that kaolinite, among the clay minerals, tends to be the principal REE carrier. They pointed out also that there is a general tendency for clay minerals to accommodate Eu2 + more easily than trivalent REE. Caggianelli et al. (1992) in studies about REE distribution in the clay fraction of pelites from the southern Apennines, Italy, show that only illite is correlated with REE, while a smectite-rich sample is characterized by the lowest content in REE. Strong correlations exist between REE and TiO2, Nb, Zr and a less significant one with Sr; no correlations exist between these elements and Y. Trace element studies in bentonites from Cabo de Gata region, Spain, were conducted by Linares et al. (1987) who calculated the
Corresponding author. E-mail addresses: [email protected], [email protected] (E. Caballero).
http://dx.doi.org/10.1016/j.clay.2017.07.028 Received 14 February 2017; Received in revised form 25 July 2017; Accepted 25 July 2017 0169-1317/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Caballero, E., Applied Clay Science (2017), http://dx.doi.org/10.1016/j.clay.2017.07.028
Applied Clay Science xxx (xxxx) xxx–xxx
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Fig. 1. Location map of the bentonite outcrop in the cabo de Gata región (SE, Spain).
Fig. 2. Geological setting and two profiles sampled.
an andesite and a rhyolite to bentonite, have also been carried out by Christidis (1998). In this study we present the content of minor and trace elements including the REE elements data for bentonite from an outcrop of Cabo de Gata region (Almeria, Spain), where volcanic dome intruded a bentonite mass producing a temperature gradient from the contact area to the exterior. The aim of this paper is to evaluate the minor, trace and
balance of major and trace elements during the process of alteration of volcanic rocks to bentonite and through statistical analysis to localize the trace elements in the bentonites. They showed that smectite retains a large proportion of the trace elements contained in the primary minerals of parent rocks in its crystal structure and hence can be very useful in order to establish the origin of bentonites. A comparative study of the mobility of major and trace elements during alteration of 2
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Table 1 Mineralogical and chemical analyses of the reference sample (RS). Total sample (%) Phyllosilicates
Plagioclase
Others
85
7
8
< 20 μm fraction (%) Smectite 89
Major elements (%) Al2O3 Fe2O3 SiO2 66.17 15.12 1.70
Biotite 11
MnO 0.11
MgO 0.20
CaO 1.20
Na2O 3.51
Trace and minor elements (ppm) Li Rb Cs Be Sr Ba Sc 21.00 136.10 12.19 6.83 108.19 166.08 3.30 Zn 35.61
Ga 17.67
Y 16.82
Nb 8.31
Ta 0.97
Yb 1.747
TiO2 0.13
P2O5 0.02
P.C. 7.01
Total 99.65
V Cr 16.26 0.00
Co 0.46
Ni 1.02
Cu 1.56
Zr Hf Mo Sn Tl Pb U 64.725 2.541 0.241 4.672 1.061 51.395 2.811
Th La Ce Pr Nd Sm 15.034 23.571 53.403 5.521 18.866 3.427 Tm 0.277
K2O 1.48
Eu Gd Tb Dy Ho 0.530 2.923 0.481 2.774 0.577
Er 1.690
Lu 0.263
the already bentonised tuffaceous materials of Frailes I. Alteration phenomena occurred in this new contact surface that are similar to those described in the contact area with the amphibole andesite of Frailes I, alternations of areas of dissolution and precipitation of mineral species. However, the presence of a thermal gave special characteristics to this new contact area. Studying this area in more depth, it can be seen that despite it being a younger contact than the interphase between bentonite and andesite materials of Frailes I, there is more penetration and intensity of the alteration area associated with the thermal contact area.
REE elements distribution pattern in the bentonite. The different behaviour in another bentonite from a stratigraphic contact area, not subject to the effect of temperature, was also studied. The comparison of profiles will enable us to see whether the changes that have occurred in the bentonite mass can be attributed to the effect of temperature or to the effect of fluids circulation. 2. Materials and methods 2.1. Material studied
2.2. Sampling and methodology
The material studied is a bentonite from an outcrop located in the Cabo de Gata Natural park (Almeria, SE Spain) (Fig. 1). In the Cabo de Gata region, volcanic activity is predominantly extrusive and the most abundant structure are dome complexes (Fernández Soler, 1992), which are connected with each other by fissures according to recognised regional fracturing systems. The different lithological groups in the area differentiated by Fernández Soler (1992) are described in Caballero et al. (2017). Previous studies about chemical and mineralogical composition carried out in these samples subjected to a thermal gradient (Caballero et al., 2017; Martínez, 2003) show that the genesis of the Cala del Tomate outcrop started around ~ 10.6 Ma (Zeck et al., 2000) with the formation in a subaerial environment of the Frailes I caldera together with tuffaceous and volcano-sedimentary andesite-type materials. The alteration of the pyroclastic materials associated with the caldera started in this environment, with the cooperation of meteoric water. This alteration mainly occurred as a result of the circulation of meteoric water benefiting the contact surfaces in the massive rock of the Frailes I caldera with associated pyroclastic products. The main alteration mechanism consisted of the circulation of fluids along the contact surfaces causing the alternation of mobilisation areas and/or dissolution of mineral species with accumulation areas and/or precipitation of these species. Later, and as a result of the fragile tectonics the area was subject to, the Frailes I caldera collapsed, leaving the volcanic materials studied in the area of influence of seawater. The fracturing that occurred during the collapse facilitates the intrusion of pyroxene andesite materials of the dome-dyke of the Cala del Tomate producing a thermal gradient in
Two sampling profiles were performed (Fig. 2). Profile CT-1, formed by a total of 14 samples taken perpendicular to the dome-bentonite contact surface, at the following distances: 0, 40, 70, 130, 200, 250, 300, 400, 600, 800, 1300, 1800, 2300 and 2800 cm with SE-NO direction. The samples were identified as follows: CT-1/1 to CT-1/14, respectively. Profile CT-2, was taken parallel to the dome-bentonite contact and perpendicular to the stratigraphic contact between the bentonised tuffaceous materials and the amphibole andesites (see Fig. 2). Ten samples were taken in this profile, which were identified as follows: CT-2/1, to CT-2/10, at distances from contact of 0, 60, 120, 220, 500, 800, 1300, 4500, 7000, 10,000 cm, respectively. The contents of minor, trace and REE in the total samples, were determined and expressed in ppm. A PERKIN ELMER Sciex-Elan 5000 mass spectrometer was used with a plasma torch ionisation source and a quadrupole ion filter. In order to study the evolution of these elements and assess the processes overlapping the bentonite formation process itself, we used diagrams normalising the concentrations found in the samples to the concentrations in a reference sample, hereafter referred to as RS. The RS selected is a bentonite with a mineralogical composition that is within the average found by several authors for the bentonites in the area (Reyes, 1977; Caballero, 1985; among others), and that was not affected by thermal processes (Table 1 shows the chemical and mineralogical composition of RS). On the other hand, in order to know the different process taking place in the samples studied, we have used 3
0 13.5 77 8.1 4.28 224 506 16.5 22.8 0.88 63.4 2.30 0.69 5.56 1.68 3.21 12.4
3.33 7.91 1.65 1.42 1.79 5.01 37.1 45.9
0 33.6 52.5 7.12 24.1 4.49 0.66 3.79 0.58 3.40 0.72 1.99 0.31 2.23 0.36
136 122 14
d (cm) Li Rb Cs Be Sr Ba Ga Y Ta Zr Hf Mo Sn Tl U Th
Sc V Cr Co Ni Cu Zn Pb
d (cm) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
∑ REE ∑ LREE ∑ HREE
T-1/1
4
126 113 13
40 28.7 54.4 6.13 20.2 3.87 0.63 3.38 0.52 2.95 0.65 1.88 0.31 2.04 0.35
3.47 7.04 0.06 1.43 1.12 5.08 21.1 24.4
40 14.7 44.6 6.8 4.75 135 293 16.5 19.7 0.88 61.1 2.25 0.31 5.08 1.39 3.47 12.5
T-1/2
126 114 12
70 26.1 60.5 5.60 18.8 3.52 0.64 3.10 0.47 2.60 0.54 1.57 0.25 1.71 0.29
4.07 18.0 0.89 3.54 2.07 5.23 26.6 89.4
70 22.7 34.4 7.2 5.10 157 356 17.6 16.8 0.91 66.3 2.37 0.21 4.02 1.37 2.73 12.6
T-1/3
Table 2 Minor, trace and rare elements (ppm).
135 121 14
130 28.9 61.1 6.25 21.2 3.89 0.60 3.52 0.55 3.40 0.71 2.02 0.33 2.31 0.38
4.00 11.0 0.17 4.32 1.88 5.08 22.1 35.7
130 18.0 26 6.7 5.10 108 127 17.6 21.7 1.23 67.7 2.45 0 4.50 1.23 4.23 13.3
T-1/4
68 62 6
200 16.2 26.2 3.75 13.0 2.35 0.48 1.88 0.30 1.50 0.31 0.82 0.13 0.89 0.13
3.04 18.2 0.80 1.11 2.12 2.72 24.2 24.6
200 15.3 109 18.2 5.78 118 109 17.1 8.1 0.95 69 2.55 0.22 6.32 2.37 2.69 15.4
T-1/5
68 62 6
250 16.2 26.2 3.75 13.0 2.35 0.48 1.88 0.30 1.60 0.31 0.84 0.13 0.83 0.13
3.10 14.0 0.30 0.62 1.10 1.42 19.0 30.8
250 19.0 30 9.8 7.17 110 34 19.5 16.9 1.01 72.7 2.94 0 6.69 0.08 0.87 16.9
T-1/6
120 109 11
300 19.5 65.2 4.75 16.0 3.10 0.56 2.67 0.47 2.80 0.60 1.82 0.30 1.96 0.30
3.42 24.0 0.00 1.09 2.12 3.18 28.4 17.2
300 14.6 59 39 6.89 117 62 19.7 17.4 1.06 75 2.85 0 7.31 0.41 1.28 17.1
T-1/7
106 96 10
400 24.2 44.8 5.25 18.3 3.36 0.57 2.78 0.44 2.50 0.49 1.41 0.22 1.46 0.23
2.49 5.72 0.00 0.33 1.22 0.98 14.2 11.0
400 10.0 352 117 5.77 293 405 15.6 14.5 0.84 59.4 2.31 0.60 5.28 2.23 4.70 13.4
T-1/8
109 98 11
600 24.4 46.1 5.42 18.8 3.44 0.60 2.87 0.45 2.50 0.54 1.60 0.26 1.68 0.25
2.40 2.68 0.00 0.36 1.87 1.23 31.1 25.0
600 15.0 276 81.4 5.16 267 403 15.2 15.1 0.79 57 2.19 0.42 4.76 1.35 4.90 12.8
T-1/9
126 113 13
800 26.8 55.9 5.90 20.5 3.81 0.61 3.11 0.53 3.30 0.71 2.02 0.33 2.02 0.31
2.80 11.8 0.00 0.66 1.75 0.94 35.2 83.9
800 10.0 230 59 6.25 248 313 16.3 19.4 0.91 62 2.4 0.48 4.92 1.47 4.18 14.2
T-1/10
116 105 11
1300 23.6 53.4 5.52 18.9 3.43 0.53 2.92 0.48 2.80 0.58 1.69 0.28 1.75 0.26
3.30 16.6 0.00 0.46 1.02 1.56 35.6 51.4
1300 21.0 136 12.2 6.83 108 166 17.7 16.8 0.97 64.7 2.54 0.24 4.67 1.06 2.81 15.0
T-1/11
125 112 13
1800 22.9 62.4 5.23 18.1 3.60 0.56 3.09 0.49 3.04 0.65 1.82 0.30 2.13 0.34
2.80 12.9 0.00 0.43 0.85 0.88 29.4 41.7
1800 25.0 261 24.4 5.81 107 248 15.8 20.2 0.88 57.2 2.25 0.42 4.72 4.32 4.10 14.0
T-1/12
113 103 10
2300 25.6 48.9 5.7 19.1 3.59 0.53 2.88 0.44 2.60 0.53 1.44 0.25 1.68 0.25
2.80 13.6 0.00 0.59 1.73 1.71 32.9 29.2
2300 36.0 367 38 6.07 131 297 15.1 16 0.85 56.5 2.17 0.47 4.73 1.84 5.26 13.5
T-1/13
108 97 11
2800 23.9 45.1 5.35 18.4 3.38 0.53 2.99 0.46 2.70 0.56 1.53 0.26 1.64 0.24
2.58 6.70 0.00 0.18 0.76 0.92 20.6 31.3
2800 12.0 296 47 5.42 280 354 14.6 16.1 0.80 54.2 2.13 0.64 4.28 0.67 5.70 13.0
T-1/14
104 95 9
0 22.6 45.9 5.12 18.0 3.25 0.54 2.60 0.39 2.20 0.47 1.25 0.20 1.28 0.20
2.37 2.78 0.00 1.54 2.38 2.23 29.3 40.9
0 36.7 141 14.4 6.32 90.9 284 16.2 13.3 0.82 61.7 2.35 0.34 4.56 4.61 4.50 13.6
T-2/1
131 120 11
60 32.1 53.7 6.85 22.7 4.18 0.66 3.51 0.53 2.92 0.56 1.53 0.24 1.57 0.25
4.64 7.65 2.30 1.33 1.79 1.37 32.9 31.1
60 56.8 114 12.5 5.56 95.8 317 16.4 15.4 0.84 67.2 2.46 0.22 4.60 3.41 4.93 12.1
T-2/2
117 106 11
120 27.1 50.2 5.79 19.5 3.61 0.59 3.21 0.48 2.51 0.54 1.49 0.24 1.50 0.24
4.70 6.65 0.00 0.98 2.01 0.83 39.6 30.7
120 45.6 131 13.8 5.22 99.3 271 16.6 15 0.88 66.2 2.44 0.36 4.90 3.90 4.82 12.4
T-2/3
113 103 10
220 26.2 48.5 5.59 18.9 3.49 0.62 3.03 0.47 2.46 0.53 1.52 0.23 1.61 0.25
4.60 2.20 0.53 0.44 1.20 0.72 31.3 20.7
220 18.5 130 48.3 5.34 267 412 16.4 15.2 0.86 64.8 2.32 0.39 4.70 1.06 5.80 12.1
T-2/4
127 115 12
500 29.0 55.2 6.25 21.0 3.80 0.67 3.24 0.50 2.77 0.56 1.56 0.24 1.57 0.25
4.57 4.19 0.91 0.95 2.62 2.28 88.0 33.3
500 42.6 78 26 5.88 188 185 17.8 15.8 0.93 70.9 2.52 0.15 4.82 0.22 5.70 13.1
T-2/5
142 130 12
800 27.1 72.2 5.93 20.5 3.78 1.78 3.02 0.48 2.66 0.55 1.57 0.25 1.70 0.26
3.10 11.6 2.74 2.38 2.07 5.17 59.0 19.9
800 28.1 28 4.8 7.12 215 654 18.5 15.5 0.95 66 2.35 0.12 5.06 1.63 5.50 14.4
T-2/6
118 109 9
1300 24.9 54.5 5.70 19.8 3.75 0.94 2.81 0.41 2.19 0.48 1.19 0.18 1.15 0.17
2.90 5.01 0.00 0.41 2.10 2.22 38.8 25.6
1300 18.6 24 4.2 5.41 148 223 17.3 11.7 0.89 65.6 2.4 0 4.40 0.19 3.65 14.5
T-2/7
111 103 8
4500 25.4 49.9 5.50 18.8 3.44 0.49 2.74 0.40 2.09 0.44 1.09 0.16 1.00 0.12
2.18 2.24 0.00 0.24 0.98 0.62 46.5 10.6
4500 7.79 114 11.8 3.54 127 38 14.4 11.7 0.76 56.9 2.2 0.65 3.55 0.52 2.92 12.8
T-2/8
115 106 9
7000 26.3 51.3 5.64 19.5 3.51 0.55 2.79 0.42 2.13 0.44 1.18 0.17 1.07 0.15
2.38 3.04 0.00 0.66 2.21 1.50 40.6 89.2
7000 4.6 121 14.2 5.26 133 64 14.2 11.7 0.78 55.8 2.11 0.12 3.40 1.05 3.73 12.9
T-2/9
117 104 13
10,000 25.2 48.6 5.69 20.5 3.98 0.68 3.46 0.53 3.12 0.67 1.92 0.30 1.95 0.27
5.04 15.7 0.00 1.46 2.41 3.22 38.7 11.5
10,000 5.06 698 21.9 5.12 151 90 15.8 19.6 0.71 60 2.23 0 3.23 0.28 3.20 10.7
T-2/10
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mobilisation, since the δ18O isotope values (Caballero et al., 2017) for these samples correlate in a contradictory manner in the two profiles. It seems, therefore, that the mobilisation of Ba needs to be explained taking into account other variables that influence the alteration process, such as the circulation of fluids, their pH, etc. Rb behaves differently near the contact compared to the rest of the profile. Rb behaviour seems to be connected with δ18O values (Caballero et al., 2017), that its distribution depends significantly on temperature and/or chemical composition. Fig. 5 shows that the Rb mobilisation area coincides with the interval of δ18O decrease. If the Rb content in the samples of profile CT-1 is compared with the δ18O values obtained, an inverse relation between Rb content and temperature is found (R2 = 0.7191), especially for the values closer to the thermal contact. With regard to profile CT-2, not significant correlation is observed (R2 = 0.0022). These results show that Rb decreases near the thermal contact where there is a temperature gradient, whilst, in the case of profile CT-2, Rb remains constant as a function of temperature. Elements as Sr could be related to temperature but it does not show any significant as Rb. HFSE elements for CT-2 profile do not show as marked fluctuations as those found in the CT-1 profile in the area near the contact. These slight fluctuations raise doubts about whether they are directly related to the proximity of the contact area or whether there are small compositional variations among the samples due to either the heterogeneity of the bentonite mass itself, or to the abundance of HFSE-rich accessory minerals. Martínez (2003) and Caballero et al. (2017), found similar results studying chemical and mineralogical composition in these bentonites. It can be deduced from the study of the evolution of incompatible LILE and HFSE elements that the effect of temperature is to cause the fractionation of the incompatible elements, thus favouring the entry into a solid phase of elements with a small radius and high charge (HFSE) compared with those with a large ionic radius (LILE). The entry of both into the solid phase increases in the area of more alteration, that is, the contact area. In areas where temperature does not have any effect, such as CT-2 profile, it is possible to see that both groups of elements mobilise in the same way. Figs. 6 and 7 show the evolution of the concentrations of transition elements depending on distance for profiles CT-1 and CT-2, respectively. Fig. 6, corresponding to the thermal contact (CT-1) shows that the maxima in Sc, Cr, Cu, Co and Ni are in the first 400 cm. Pb shows two maxima, at 70 and 800 cm, respectively. A second axis of ordinates had been used for elements V and Ni in Fig. 7, corresponding to the contact for profile CT-2, where it can be observed that the most important fluctuations also occur near the contact. Although there is a maximum in Cr, Cu, Co, Pb and V in the sample at 800 cm, this maximum does not represent a profile trend and is considered as an isolated behaviour. Both figures again show that the most important fluctuations of the transition elements are located in areas near both contacts. Compatible elements are those which have varied their concentrations more intensely as a result of the proximity of a supergene alteration zone connected with a contact area. Figs. 8 and 9 show the concentrations of light (La-Eu) and heavy (Gd-Lu) (REE) for both profiles (CT-1 and CT-2). The parallel evolution of light and heavy REE shows that no fractionation occurs between them. Nevertheless, values for the thermal contact (profile CT-1) show a more marked mobilisation of REE than those produced in the contact for profile CT-2. The Coryell-Masuda diagrams for the profiles studied (Figs. 8 and 9) show that the proximity of a thermal contact area does not cause substantial changes in the distribution of the REE of the bentonite samples. This behaviour is similar to that of a typical model of sedimentary rocks (Chondrite-normalized REE diagrams for sediments and sedimentary rocks) (McLennan, 1989) although with less enrichment in La. Elements such as Eu and Ce have small variations compared with chondrite and andesite normalized patterns (Fig. 8a and b). The most marked
Fig. 3. Evolution of the LILE and HFSE elements depending on distance for profile CT-1 corresponding to the termal contact.
profiles normalized to chondrite (Evensen et al., 1978) (a), andesite (Taylor and McLennan, 1985) (b), and the RS (c).
3. Results and discussion Minor, trace and REE in the total sample are detailed in Table 2. Figs. 3 and 4 show a comparison of values of Light Elements Lithofile Elements (LILE) compared with High Field Strong Elements (HFSE) elements for both profiles. CT-1 profile in the first 400 cm (Fig. 3) shows that the LILE elements are at a minimum compared with the maximum of the HFSE. Sr presents a maximum value of 267 ppm at 220 cm from the contact, decreasing gradually until 150 ppm with distance. Rb has the highest concentrations near the contact, with values around 130 ppm, and gradually decreases with distance, showing average values of 75 ppm. For the CT-2 profile (Fig. 4), the first observation that can be made is that there is not a homogenous pattern of lithophile elements near the contact, as it occurred in profile CT-1. In profile CT-2 it is not possible to detect any fractionation of the lithophile elements near the contact. Barium shows anomalous behaviour with a very high maximum of 650 ppm at 800 cm, in comparison to with the average Ba value calculated for the entire outcrop (207 ppm). This highlights that Ba is sensitive to the alteration processes that have taken place in the profiles studied, in accordance with Christidis (1998) who found Ba to be relatively stable in the first stages of alteration, but to display a sudden increase in concentration in a more advanced stages. Nevertheless, temperature does not seem to be the only factor responsible for Ba 5
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Fig. 4. Evolution of the LILE (a) and HFSE (b) elements depending on distance for profile CT-2 corresponding to stratigraphical contact.
anomalies are observed in comparison with the RS (Figs. 8c and 9c). This would mean that the processes which caused those anomalies would have occurred after the formation process of bentonite. The negative anomaly in Ce observed in the samples near the contact areas could be indicative of the participation of seawater mobilised in favour of these surfaces (McLennan, 1989, 1999; Shikazono et al., 2008). On the other hand, Eu under reducing conditions behaves in a similar fashion to the calc-alkaline elements Ca and Sr, so it can replace both behaving in a less incompatible manner (Richardson and McSween, 1989). These values are characteristic of reducing conditions, which indicates that the bentonite process formation occurred in supergene conditions in this case. Shikazono et al. (2008) in studies about geochemical behaviour of rare elements in hydrothermal altered rocks, found a negative Eu anomaly as a result of leaching of Eu2 + by reducing hydrothermal solutions.
Fig. 5. Evolution of Rb (ppm) against oxygen stable isotope composition (smow).
6
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Fig. 6. Evolution of the transition elements Sc, Cr, Cu, Co, Ni, V, Zn and Pb depending on distance for profile CT-1 corresponding to thermal contact.
Fig. 8. The Coryell-Masuda diagrams for the profile CT-1 (thermal contact) normalized to chondrite (a), andesite (b) and reference simple (c). Legend shows distance (cm) from contact to samples.
Taking into account the above considerations, the profiles should follow a pattern that shows that the areas near the contact, where the rock has been in the presence of seawater (Ce/Ce* < 1) are also where the lowest values of Eu/Eu* should be measured. These premises are met in the case of profile CT-2 (Fig. 10b), except for the samples located at 800 and 1300 cm, where both the Ce/Ce* and Eu/Eu* values are abnormally high. The anomaly in Eu in these samples may be related to the high concentrations of Ba present (over 5000 ppm above average), since both elements have a similar ionic radius and identical coordination. Similar behaviour was reported by McLennan (1999), and Richardson and McSween (1989), who described the replacement of Eu by Sr and/or by Ca in the feldspar structure. According to Hurlbut and Klein (1991), high concentrations of Ba together with Pb, Cu, Co and Mn are associated with minerals such as hyalophane, manganese, barite, siderite, etc., in connection with a hydrothermal vein. These data correspond to high concentrations of Mg, Mn, Fe, Co, Pb, Cr, Cu and Mo present in the 800 cm sample, which significantly exceeded the deposit average concentration, and which could be connected with vein mineralisations, such as those described above. Therefore, it is feasible to believe that profile CT-2 crosses a small hydrothermal vein at around 800 cm away from the stratigraphic contact, which would explain the abnormally high concentrations of the various trace elements. According to McLennan (1999), Ce and Mn are intimately related. It is not, therefore, surprising that Ce is also enriched at 800 cm from the stratigraphical contact, where there are abnormally high concentrations
Fig. 7. Evolution of the transition elements Sc, Cr, Cu, Co, Ni, V, Zn and Pb depending on distance for profile CT-2 corresponding to the stratigraphical contact.
7
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Fig. 9. The Coryell-Masuda diagrams for the profile CT-2 (stratigraphical contact) normalized to chondrite (a), andesite (b) and reference simple (c). Legend shows distance (cm) from contact to samples.
Fig. 10. Evolution of the Ce/Ce* and Eu/Eu* relations versus distance (cm) for profile CT-1 corresponding to the termal contact (a) and for profile CT-2 corresponding to the estratigraphical contact (b).
8
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Fig. 11. Fractionation for heavy, intermediate and light REE versus distance from both contacts: a) Thermal contact (CT-1) and b) stratigraphical contact (CT-2). La/Lu relation is plotted in the secondary axis.
4. Conclusions
of Mn (several times above the average). In the case of profile CT-1 represented in Fig. 10a, it can be seen that two maxima occur in the Ce/Ce* relation at a distance of 70 and 300 cm from the thermal contact. The one at 70 cm coincides with the Mn maximum in the profile (analogue situation to that of profile CT-2) and the 300 cm maximum coincides with an area of accumulation, where smectite is being generated, and, therefore, where the various elements that have been mobilised in the areas near the contact are deposited. Fig. 11a and b shows that the fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE) has fluctuations in areas close to both types of contact. Fractionation occurs homogeneously, showing a parallel evolution between them, which is constant throughout the profile. Only the La/Nd relation has a behaviour different for the rest in the first 600 cm of contact. This is because the large ionic radius characteristic of LREE and their high charge make them the most incompatible in the entire group. They only form part of very open structures, such as those formed mainly by sedimentary minerals (McLennan, 1999). It can be seen from these graphs (Fig. 11) that, compared with the Sm/Dy and Ho/Lu relations, the La/Nd one increased in the areas that have suffered more alteration, favoured by the availability of fluids due to their closeness to the contact area. By contrast, in the areas where leaching of neoformed sedimentary minerals has occurred due to the circulation of fluids in the area close to the contact, the La/Nd relation decreased compared with the Sm/Dy and Ho/Lu relations. These fluid circulation areas are favoured by the presence of a thermal gradient (Fig. 11a). These observations concur with those made in the study of Eu/Eu* and Ce/Ce* relations. Therefore, the effect of temperature caused mobilisation of rare earth elements. This mobilisation became obvious when studying the behaviour of all the rare earth elements (∑ REE) with distance to the different contacts. The evolution of transition elements represented by Cu and V followed the same trend as that observed in rare earth elements. The availability of fluids near the contact area encourages the incorporation of these elements. This availability becomes more intense with temperature, which leads to more element enrichment (Table 2).
The study of trace elements and rare earth behaviour allowed to know the degree of the alteration in the bentonite. It has been shown that there are no major differences in the REE distribution of bentonite subjected to a thermal contact area in front of a stratigraphic contact zone. Also, there are no significant differences with the REE pattern of andesite obtained by Taylor and McLennan (1985). The differences found are consistent with the differences described for supergene alteration processes. These similarities in the patterns indicate that the processes of bentonitization and later alteration related to the contact in Cala del Tomate outcrop, do not involve a significant transformation in the pattern of rare earths. On the whole, the presence of a contact area causes element mobilisation. This mobilisation, depending on whether there is a temperature gradient, occurs more intensely and penetrates further into the bentonite, in other words, it leads to quantitative differences. On the other hand, there are elements whose behaviour depends directly on temperature, so they behave as qualitative indicators of its action in the system. Consequently, Rb mobilises significantly near a thermal contact, following a pattern that contrasts with its behaviour in a mechanical contact. Other elements that are sensitive to the effect of temperature are lithophile elements. These elements describe a fractionation of LILE compared with HFSE near the thermal contact. The main chemical differences between thermal contact and stratigraphic contact area are not subjected to the effect of temperature is the incorporation of trace elements with a small radius (HFSE) in the structure of the smectites subject to the effect of temperature, in detriment of those with a larger radius (LILE). It can be deduced from the study of the evolution of incompatible LILE and HFSE elements that the effect of the temperature that has acted on the bentonite mass causes the fractionation of the incompatible elements, thus favouring the entry into a solid phase of elements with a small radius and high charge (HFSE) compared with those with a large ionic radius (LILE). When temperature does not have any control, such as the case of profile CT-2, it is possible to see that 9
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Martínez, J.A., 2003. Comportamiento fisico-químico de la bentonite bajo condiciones naturales de temperature y pH. In: Análogo natural del almacenamiento geológico profundo. University of Granada, Spain Ph. D. thesis. McLennan, S.M., 1989. Rare earth elements in sedimentary rocks: influence of provenance and sedimentary processes. In: Lipin, B.R., Mckay, G.A. (Eds.), Geochemistry and Mineralogy of Rare Earth Elements. vol. 21. Mineralogical Society of America, Washington, DC, pp. 169–200 (Reviews in Mineralogy). McLennan, S.M., 1999. Elements: lanthanide series, rare earth. In: Marschall, C.P., Fairbridge, R.W. (Eds.), Encyclopedie of Geochemistry. Kluwer Academic Publishers, pp. 211–213. Muchangos, A.C., 2006. The mobility of rare-earth and other elements in the process of alteration of rhyolitic rocks to bentonite (Lebombo Volcanic Mountainous Chain, Mozambique). J. Geochem. Explor. 88, 300–303. Özdamar, S., Ece, Ö.I., Uz, B., Boylu, F., Ercan, H.Ü., Yanik, G., 2014. Element mobility during the formation of the Uzunisa-Ordu bentonite, NE Turkey, and potential applications. Clay Miner. 49, 609–633. Prudencio, M.J., Figueiredo, M.O., Cabral, J.M.P., 1989. Rare earth distribution and its correlation with clay mineralogy in the clay-sized fraction of Cretaceous and Pliocene sediments (central Portugal). Clay Miner. 24, 67–74. Reyes, E., 1977. Mineralogía y geoquímica de las bentonitas de la zona norte de Cabo de Gata (Almería). PhD thesis University of Granada, Spain (452 pp.). Richardson, S.M., McSween, H.Y.Jr, 1989. The crust and mantle as a geochemical system. In: Richarson, McSween (Eds.), Geochemistry, Patways and Processes. Prentice Hall, New Jersey, pp. 327–373. Shikazono, N., Ogawa, Y., Utada, M., Ishiyama, D., Mizuta, T., Ishikawa, N., Kubota, Y., 2008. Geochemical behavior of rare elements in hydrothermally altered rocks of the Kuroko mining área, Japan. J. Geochem. Explor. 98, 65–79. Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution; an Examination of Geochemical Record Preserved in Sedimentary Rocks. Blackwell Scientific, Oxford (312 pp.). Thompson, G.M., Malpas, J., 2000. Mineral/melt partition coefficients of oceanic álcali basalts determine don natural samples using laser ablation-inductively coupled plasma-mass spectrometry (LAM-ICP-MS). Min. Mag. 64, 85–94. Tiepolo, M., Tribuzio, R., Vannucci, R., 2002. The compositions of mantle –derived Meles developed Turing the Alpine continental collision. Contrib. Mineral. Petrol. 144, 1–15. Wood, B.J., Blundy, J.D., 1997. A predictive model for rare earth element partitioning between clinopyroxene and anhydrous silicate melt. Contrib. Mineral. Petrol. 129, 166–181. Wood, B.J., Blundy, J.D., 2001. The effect of cation charge on crystal-melt partitioning of trace elements. Earth Planet. Sci. Lett. 188, 59–71. Zeck, H.P., Maluski, H., Kristensen, A.B., 2000. Revised geochronology of Neogene calcalkaline volcanic suite in Sierra de Gata, Alborán volcanic province, SE Spain. J. Geol. Soc. 157, 71–81.
both groups of elements mobilise in the same way. The entry of both into the solid phase increases in the area of more alteration, which, in this case, is the contact area. Acknowledgements The authors are grateful to A. Caballero for his graphical assistance. References Arslan, M., Abdioglu, E., Kadir, S., 2010. Mineralogy, geochemistry, and origin of bentonite in Upper Cretaceous pyroclastic units of the Tirebolu area, Giresun, Northeast Turkey. Clay Clay Miner. 58 (1), 120–141. Banfield, J.F., Eggleton, R.A., 1989. Apatite replacement and rare earth mobilization, fractionation and fixation during weathering. Clay Clay Miner. 38, 77–89. Caballero, E., 1985. Quimismo del proceso de bentonitización en la región volcánica de Cabo de Gata (Almería). Ph.D. thesis University of Granada, Spain (339 pp.). Caballero, E., Jiménez de Cisneros, C., Martinez, J.A., 2017. Thermal alteration in a bentonite from Cabo de Gata, Almería, SE Spain. Chem. Erde (in revision). Caggianelli, A., Fiore, S., Mongelli, G., Salvemini, A., 1992. REE distribution in the clay fraction of pelites from the southern Apennines, Italy. Chem. Geol. 99, 253–263. Christidis, G.E., 1998. Comparative study of the mobilityof major and trace elements during alteration of an andesite and a rhyolite to bentonite, in the islands of Milos and Kimolos, Aegean, Greece. Clay Clay Miner. 46 (4), 379–399. Coogan, L.A., Kempton, P.D., Saunders, A.D., Norry, M.J., 2000. Melt aggregation within the crust beneath the Mid-Atlantic Ridge: evidence from plagioclase and clynopyroxene major and trace element compositions. Earth Plan. Sci. Lett. 176, 245–257. Cullers, R.L., Chaudhuri, S., Kilbane, N., Koch, R., 1979. Rare earths in size fraction and sedimentary rocks of Pennsylvanian-Permian age from the mid-continent of the USA. Geochim. Cosmochim. Acta 43, 1285–1302. Evensen, N.M., Hamilton, P.J., O'Nions, R.K., 1978. Rare-earth abundances in chondritic meteorites. Geochim. Cosmochim. Acta 42, 1199–1212. Fernández Soler, J.M., 1992. El volcanismo calco-alcalino de Cabo de Gata (Almería). Ph.D. thesis University of Granada, Spain. Hurlbut, C.S.Jr., Klein, C., 1991. In: Reverté, S.A. (Ed.), Manual de mineralogía de Dana. Linares, J., Caballero, E., Reyes, E., Huertas, F., 1987. Trace element mobility in bentonite formation. In: Hurst, R.W., Davis, T.E., Augustithis, S.S. (Eds.), The Practical Applications of Trace Elements and Isotopes to Environmental Biogeochemistry and Mineral Resources Evaluation. Theophrastus Publication, S.A., pp. 233–250. Marks, M., Halama, R., Wenzel, T., Markl, Gregor, 2004. Trace element variations in clinopyroxene and amphibole from alkaline to peralkaline syenites and granites: implications for mineral-melt trace-element partitioning. Chem. Geol. 211, 185–215.
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Research paper
Partitioning of minor, trace elements and rare earth elements in bentonite affecting by thermal alteration E. Caballero⁎, C. Jiménez de Cisneros Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Avda. de las Palmeras, 4, 18100 Armilla, Granada, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords: Minor elements Trace elements Rare earth element Bentonite Cabo de Gata (Almería Spain)
Minor and trace elements, included the rare earth elements (REE), of bentonite that has undergone the natural action of a thermal alteration have been determined. This study has been conducted in the Cala del Tomate outcrop, Cabo de Gata region (Almeria Spain), where an important volcanic dome has intruded in a bentonite mass producing a temperature gradient from the contact area to the exterior. Data are compared with those obtained in bentonites that not were subjected to the thermal effect. No major differences in the REE distribution of bentonite subjected to a thermal contact area in front of a stratigraphic contact zone have been found. On the whole, the contact metamorphism causes element mobilisation, depending on whether there is a temperature gradient. Elements whose behaviour depends directly on temperature, behave as qualitative indicators of element mobility. Rb mobilises significantly near a thermal contact, a pattern that contrasts with its behaviour in a mechanical contact. Other elements that are sensitive to the effect of temperature are lithophile elements. These elements demonstrate a fractionation of Light Elements Lithofile Elements (LILE) compared with High Field Strong Elements (HFSE) near the thermal contact. The main chemical differences with the stratigraphic contact area not subject to the effect of temperature are the incorporation of trace elements with a small radius (HSFE) in the structure of the smectites subject to the effect of temperature, to the detriment of those with a larger radius (LILE).
1. Introduction Several studies show that crystal chemistry exerts a major control on trace element partitioning (Wood and Blundy, 1997, 2001). Marks et al. (2004) compared the trace element contents of mafic minerals in order to investigate the partitioning behaviour of trace elements in natural alkaline silicate melts. Trace elements determination in basaltic systems have been developed by Coogan et al. (2000); Thompson and Malpas (2000); Tiepolo et al. (2002), in hydrothermally altered rocks by Shikazono et al. (2008), in process of alteration of rhyolitic rocks to bentonite by Muchangos (2006) and element mobility during the bentonite formation have been studied by Özdamar et al. (2014). In most minerals, trace elements fill lattice sites by replacing the main element of the lattice. They can be precipitated within cracks of the crystal in special composition. Although the level of trace elements is as low as parts per thousand (ppt), and part per million (ppm) in soil or rocks, they can provide useful metal deposits which can have economical importance. Rare earth elements (REE) in sedimentary rocks concentrate in the silt and clay fractions and their contents appear uncorrelated with clay
⁎
mineralogy (Cullers et al., 1979). The differences in the REE content may be inherited from the REE composition of the source rock or determined by chemical weathering processes in the source area (Banfield and Eggleton, 1989). Generally, the incompatible element composition of bentonites is similar to that of the surrounding volcanic rocks, suggesting that the incompatible elements were generally immobile during alteration processes (Arslan et al., 2010). REE distribution in the clay fraction of sediments from central Portugal was studied by Prudencio et al. (1989) who suggested that kaolinite, among the clay minerals, tends to be the principal REE carrier. They pointed out also that there is a general tendency for clay minerals to accommodate Eu2 + more easily than trivalent REE. Caggianelli et al. (1992) in studies about REE distribution in the clay fraction of pelites from the southern Apennines, Italy, show that only illite is correlated with REE, while a smectite-rich sample is characterized by the lowest content in REE. Strong correlations exist between REE and TiO2, Nb, Zr and a less significant one with Sr; no correlations exist between these elements and Y. Trace element studies in bentonites from Cabo de Gata region, Spain, were conducted by Linares et al. (1987) who calculated the
Corresponding author. E-mail addresses: [email protected], [email protected] (E. Caballero).
http://dx.doi.org/10.1016/j.clay.2017.07.028 Received 14 February 2017; Received in revised form 25 July 2017; Accepted 25 July 2017 0169-1317/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Caballero, E., Applied Clay Science (2017), http://dx.doi.org/10.1016/j.clay.2017.07.028
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Fig. 1. Location map of the bentonite outcrop in the cabo de Gata región (SE, Spain).
Fig. 2. Geological setting and two profiles sampled.
an andesite and a rhyolite to bentonite, have also been carried out by Christidis (1998). In this study we present the content of minor and trace elements including the REE elements data for bentonite from an outcrop of Cabo de Gata region (Almeria, Spain), where volcanic dome intruded a bentonite mass producing a temperature gradient from the contact area to the exterior. The aim of this paper is to evaluate the minor, trace and
balance of major and trace elements during the process of alteration of volcanic rocks to bentonite and through statistical analysis to localize the trace elements in the bentonites. They showed that smectite retains a large proportion of the trace elements contained in the primary minerals of parent rocks in its crystal structure and hence can be very useful in order to establish the origin of bentonites. A comparative study of the mobility of major and trace elements during alteration of 2
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Table 1 Mineralogical and chemical analyses of the reference sample (RS). Total sample (%) Phyllosilicates
Plagioclase
Others
85
7
8
< 20 μm fraction (%) Smectite 89
Major elements (%) Al2O3 Fe2O3 SiO2 66.17 15.12 1.70
Biotite 11
MnO 0.11
MgO 0.20
CaO 1.20
Na2O 3.51
Trace and minor elements (ppm) Li Rb Cs Be Sr Ba Sc 21.00 136.10 12.19 6.83 108.19 166.08 3.30 Zn 35.61
Ga 17.67
Y 16.82
Nb 8.31
Ta 0.97
Yb 1.747
TiO2 0.13
P2O5 0.02
P.C. 7.01
Total 99.65
V Cr 16.26 0.00
Co 0.46
Ni 1.02
Cu 1.56
Zr Hf Mo Sn Tl Pb U 64.725 2.541 0.241 4.672 1.061 51.395 2.811
Th La Ce Pr Nd Sm 15.034 23.571 53.403 5.521 18.866 3.427 Tm 0.277
K2O 1.48
Eu Gd Tb Dy Ho 0.530 2.923 0.481 2.774 0.577
Er 1.690
Lu 0.263
the already bentonised tuffaceous materials of Frailes I. Alteration phenomena occurred in this new contact surface that are similar to those described in the contact area with the amphibole andesite of Frailes I, alternations of areas of dissolution and precipitation of mineral species. However, the presence of a thermal gave special characteristics to this new contact area. Studying this area in more depth, it can be seen that despite it being a younger contact than the interphase between bentonite and andesite materials of Frailes I, there is more penetration and intensity of the alteration area associated with the thermal contact area.
REE elements distribution pattern in the bentonite. The different behaviour in another bentonite from a stratigraphic contact area, not subject to the effect of temperature, was also studied. The comparison of profiles will enable us to see whether the changes that have occurred in the bentonite mass can be attributed to the effect of temperature or to the effect of fluids circulation. 2. Materials and methods 2.1. Material studied
2.2. Sampling and methodology
The material studied is a bentonite from an outcrop located in the Cabo de Gata Natural park (Almeria, SE Spain) (Fig. 1). In the Cabo de Gata region, volcanic activity is predominantly extrusive and the most abundant structure are dome complexes (Fernández Soler, 1992), which are connected with each other by fissures according to recognised regional fracturing systems. The different lithological groups in the area differentiated by Fernández Soler (1992) are described in Caballero et al. (2017). Previous studies about chemical and mineralogical composition carried out in these samples subjected to a thermal gradient (Caballero et al., 2017; Martínez, 2003) show that the genesis of the Cala del Tomate outcrop started around ~ 10.6 Ma (Zeck et al., 2000) with the formation in a subaerial environment of the Frailes I caldera together with tuffaceous and volcano-sedimentary andesite-type materials. The alteration of the pyroclastic materials associated with the caldera started in this environment, with the cooperation of meteoric water. This alteration mainly occurred as a result of the circulation of meteoric water benefiting the contact surfaces in the massive rock of the Frailes I caldera with associated pyroclastic products. The main alteration mechanism consisted of the circulation of fluids along the contact surfaces causing the alternation of mobilisation areas and/or dissolution of mineral species with accumulation areas and/or precipitation of these species. Later, and as a result of the fragile tectonics the area was subject to, the Frailes I caldera collapsed, leaving the volcanic materials studied in the area of influence of seawater. The fracturing that occurred during the collapse facilitates the intrusion of pyroxene andesite materials of the dome-dyke of the Cala del Tomate producing a thermal gradient in
Two sampling profiles were performed (Fig. 2). Profile CT-1, formed by a total of 14 samples taken perpendicular to the dome-bentonite contact surface, at the following distances: 0, 40, 70, 130, 200, 250, 300, 400, 600, 800, 1300, 1800, 2300 and 2800 cm with SE-NO direction. The samples were identified as follows: CT-1/1 to CT-1/14, respectively. Profile CT-2, was taken parallel to the dome-bentonite contact and perpendicular to the stratigraphic contact between the bentonised tuffaceous materials and the amphibole andesites (see Fig. 2). Ten samples were taken in this profile, which were identified as follows: CT-2/1, to CT-2/10, at distances from contact of 0, 60, 120, 220, 500, 800, 1300, 4500, 7000, 10,000 cm, respectively. The contents of minor, trace and REE in the total samples, were determined and expressed in ppm. A PERKIN ELMER Sciex-Elan 5000 mass spectrometer was used with a plasma torch ionisation source and a quadrupole ion filter. In order to study the evolution of these elements and assess the processes overlapping the bentonite formation process itself, we used diagrams normalising the concentrations found in the samples to the concentrations in a reference sample, hereafter referred to as RS. The RS selected is a bentonite with a mineralogical composition that is within the average found by several authors for the bentonites in the area (Reyes, 1977; Caballero, 1985; among others), and that was not affected by thermal processes (Table 1 shows the chemical and mineralogical composition of RS). On the other hand, in order to know the different process taking place in the samples studied, we have used 3
0 13.5 77 8.1 4.28 224 506 16.5 22.8 0.88 63.4 2.30 0.69 5.56 1.68 3.21 12.4
3.33 7.91 1.65 1.42 1.79 5.01 37.1 45.9
0 33.6 52.5 7.12 24.1 4.49 0.66 3.79 0.58 3.40 0.72 1.99 0.31 2.23 0.36
136 122 14
d (cm) Li Rb Cs Be Sr Ba Ga Y Ta Zr Hf Mo Sn Tl U Th
Sc V Cr Co Ni Cu Zn Pb
d (cm) La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
∑ REE ∑ LREE ∑ HREE
T-1/1
4
126 113 13
40 28.7 54.4 6.13 20.2 3.87 0.63 3.38 0.52 2.95 0.65 1.88 0.31 2.04 0.35
3.47 7.04 0.06 1.43 1.12 5.08 21.1 24.4
40 14.7 44.6 6.8 4.75 135 293 16.5 19.7 0.88 61.1 2.25 0.31 5.08 1.39 3.47 12.5
T-1/2
126 114 12
70 26.1 60.5 5.60 18.8 3.52 0.64 3.10 0.47 2.60 0.54 1.57 0.25 1.71 0.29
4.07 18.0 0.89 3.54 2.07 5.23 26.6 89.4
70 22.7 34.4 7.2 5.10 157 356 17.6 16.8 0.91 66.3 2.37 0.21 4.02 1.37 2.73 12.6
T-1/3
Table 2 Minor, trace and rare elements (ppm).
135 121 14
130 28.9 61.1 6.25 21.2 3.89 0.60 3.52 0.55 3.40 0.71 2.02 0.33 2.31 0.38
4.00 11.0 0.17 4.32 1.88 5.08 22.1 35.7
130 18.0 26 6.7 5.10 108 127 17.6 21.7 1.23 67.7 2.45 0 4.50 1.23 4.23 13.3
T-1/4
68 62 6
200 16.2 26.2 3.75 13.0 2.35 0.48 1.88 0.30 1.50 0.31 0.82 0.13 0.89 0.13
3.04 18.2 0.80 1.11 2.12 2.72 24.2 24.6
200 15.3 109 18.2 5.78 118 109 17.1 8.1 0.95 69 2.55 0.22 6.32 2.37 2.69 15.4
T-1/5
68 62 6
250 16.2 26.2 3.75 13.0 2.35 0.48 1.88 0.30 1.60 0.31 0.84 0.13 0.83 0.13
3.10 14.0 0.30 0.62 1.10 1.42 19.0 30.8
250 19.0 30 9.8 7.17 110 34 19.5 16.9 1.01 72.7 2.94 0 6.69 0.08 0.87 16.9
T-1/6
120 109 11
300 19.5 65.2 4.75 16.0 3.10 0.56 2.67 0.47 2.80 0.60 1.82 0.30 1.96 0.30
3.42 24.0 0.00 1.09 2.12 3.18 28.4 17.2
300 14.6 59 39 6.89 117 62 19.7 17.4 1.06 75 2.85 0 7.31 0.41 1.28 17.1
T-1/7
106 96 10
400 24.2 44.8 5.25 18.3 3.36 0.57 2.78 0.44 2.50 0.49 1.41 0.22 1.46 0.23
2.49 5.72 0.00 0.33 1.22 0.98 14.2 11.0
400 10.0 352 117 5.77 293 405 15.6 14.5 0.84 59.4 2.31 0.60 5.28 2.23 4.70 13.4
T-1/8
109 98 11
600 24.4 46.1 5.42 18.8 3.44 0.60 2.87 0.45 2.50 0.54 1.60 0.26 1.68 0.25
2.40 2.68 0.00 0.36 1.87 1.23 31.1 25.0
600 15.0 276 81.4 5.16 267 403 15.2 15.1 0.79 57 2.19 0.42 4.76 1.35 4.90 12.8
T-1/9
126 113 13
800 26.8 55.9 5.90 20.5 3.81 0.61 3.11 0.53 3.30 0.71 2.02 0.33 2.02 0.31
2.80 11.8 0.00 0.66 1.75 0.94 35.2 83.9
800 10.0 230 59 6.25 248 313 16.3 19.4 0.91 62 2.4 0.48 4.92 1.47 4.18 14.2
T-1/10
116 105 11
1300 23.6 53.4 5.52 18.9 3.43 0.53 2.92 0.48 2.80 0.58 1.69 0.28 1.75 0.26
3.30 16.6 0.00 0.46 1.02 1.56 35.6 51.4
1300 21.0 136 12.2 6.83 108 166 17.7 16.8 0.97 64.7 2.54 0.24 4.67 1.06 2.81 15.0
T-1/11
125 112 13
1800 22.9 62.4 5.23 18.1 3.60 0.56 3.09 0.49 3.04 0.65 1.82 0.30 2.13 0.34
2.80 12.9 0.00 0.43 0.85 0.88 29.4 41.7
1800 25.0 261 24.4 5.81 107 248 15.8 20.2 0.88 57.2 2.25 0.42 4.72 4.32 4.10 14.0
T-1/12
113 103 10
2300 25.6 48.9 5.7 19.1 3.59 0.53 2.88 0.44 2.60 0.53 1.44 0.25 1.68 0.25
2.80 13.6 0.00 0.59 1.73 1.71 32.9 29.2
2300 36.0 367 38 6.07 131 297 15.1 16 0.85 56.5 2.17 0.47 4.73 1.84 5.26 13.5
T-1/13
108 97 11
2800 23.9 45.1 5.35 18.4 3.38 0.53 2.99 0.46 2.70 0.56 1.53 0.26 1.64 0.24
2.58 6.70 0.00 0.18 0.76 0.92 20.6 31.3
2800 12.0 296 47 5.42 280 354 14.6 16.1 0.80 54.2 2.13 0.64 4.28 0.67 5.70 13.0
T-1/14
104 95 9
0 22.6 45.9 5.12 18.0 3.25 0.54 2.60 0.39 2.20 0.47 1.25 0.20 1.28 0.20
2.37 2.78 0.00 1.54 2.38 2.23 29.3 40.9
0 36.7 141 14.4 6.32 90.9 284 16.2 13.3 0.82 61.7 2.35 0.34 4.56 4.61 4.50 13.6
T-2/1
131 120 11
60 32.1 53.7 6.85 22.7 4.18 0.66 3.51 0.53 2.92 0.56 1.53 0.24 1.57 0.25
4.64 7.65 2.30 1.33 1.79 1.37 32.9 31.1
60 56.8 114 12.5 5.56 95.8 317 16.4 15.4 0.84 67.2 2.46 0.22 4.60 3.41 4.93 12.1
T-2/2
117 106 11
120 27.1 50.2 5.79 19.5 3.61 0.59 3.21 0.48 2.51 0.54 1.49 0.24 1.50 0.24
4.70 6.65 0.00 0.98 2.01 0.83 39.6 30.7
120 45.6 131 13.8 5.22 99.3 271 16.6 15 0.88 66.2 2.44 0.36 4.90 3.90 4.82 12.4
T-2/3
113 103 10
220 26.2 48.5 5.59 18.9 3.49 0.62 3.03 0.47 2.46 0.53 1.52 0.23 1.61 0.25
4.60 2.20 0.53 0.44 1.20 0.72 31.3 20.7
220 18.5 130 48.3 5.34 267 412 16.4 15.2 0.86 64.8 2.32 0.39 4.70 1.06 5.80 12.1
T-2/4
127 115 12
500 29.0 55.2 6.25 21.0 3.80 0.67 3.24 0.50 2.77 0.56 1.56 0.24 1.57 0.25
4.57 4.19 0.91 0.95 2.62 2.28 88.0 33.3
500 42.6 78 26 5.88 188 185 17.8 15.8 0.93 70.9 2.52 0.15 4.82 0.22 5.70 13.1
T-2/5
142 130 12
800 27.1 72.2 5.93 20.5 3.78 1.78 3.02 0.48 2.66 0.55 1.57 0.25 1.70 0.26
3.10 11.6 2.74 2.38 2.07 5.17 59.0 19.9
800 28.1 28 4.8 7.12 215 654 18.5 15.5 0.95 66 2.35 0.12 5.06 1.63 5.50 14.4
T-2/6
118 109 9
1300 24.9 54.5 5.70 19.8 3.75 0.94 2.81 0.41 2.19 0.48 1.19 0.18 1.15 0.17
2.90 5.01 0.00 0.41 2.10 2.22 38.8 25.6
1300 18.6 24 4.2 5.41 148 223 17.3 11.7 0.89 65.6 2.4 0 4.40 0.19 3.65 14.5
T-2/7
111 103 8
4500 25.4 49.9 5.50 18.8 3.44 0.49 2.74 0.40 2.09 0.44 1.09 0.16 1.00 0.12
2.18 2.24 0.00 0.24 0.98 0.62 46.5 10.6
4500 7.79 114 11.8 3.54 127 38 14.4 11.7 0.76 56.9 2.2 0.65 3.55 0.52 2.92 12.8
T-2/8
115 106 9
7000 26.3 51.3 5.64 19.5 3.51 0.55 2.79 0.42 2.13 0.44 1.18 0.17 1.07 0.15
2.38 3.04 0.00 0.66 2.21 1.50 40.6 89.2
7000 4.6 121 14.2 5.26 133 64 14.2 11.7 0.78 55.8 2.11 0.12 3.40 1.05 3.73 12.9
T-2/9
117 104 13
10,000 25.2 48.6 5.69 20.5 3.98 0.68 3.46 0.53 3.12 0.67 1.92 0.30 1.95 0.27
5.04 15.7 0.00 1.46 2.41 3.22 38.7 11.5
10,000 5.06 698 21.9 5.12 151 90 15.8 19.6 0.71 60 2.23 0 3.23 0.28 3.20 10.7
T-2/10
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mobilisation, since the δ18O isotope values (Caballero et al., 2017) for these samples correlate in a contradictory manner in the two profiles. It seems, therefore, that the mobilisation of Ba needs to be explained taking into account other variables that influence the alteration process, such as the circulation of fluids, their pH, etc. Rb behaves differently near the contact compared to the rest of the profile. Rb behaviour seems to be connected with δ18O values (Caballero et al., 2017), that its distribution depends significantly on temperature and/or chemical composition. Fig. 5 shows that the Rb mobilisation area coincides with the interval of δ18O decrease. If the Rb content in the samples of profile CT-1 is compared with the δ18O values obtained, an inverse relation between Rb content and temperature is found (R2 = 0.7191), especially for the values closer to the thermal contact. With regard to profile CT-2, not significant correlation is observed (R2 = 0.0022). These results show that Rb decreases near the thermal contact where there is a temperature gradient, whilst, in the case of profile CT-2, Rb remains constant as a function of temperature. Elements as Sr could be related to temperature but it does not show any significant as Rb. HFSE elements for CT-2 profile do not show as marked fluctuations as those found in the CT-1 profile in the area near the contact. These slight fluctuations raise doubts about whether they are directly related to the proximity of the contact area or whether there are small compositional variations among the samples due to either the heterogeneity of the bentonite mass itself, or to the abundance of HFSE-rich accessory minerals. Martínez (2003) and Caballero et al. (2017), found similar results studying chemical and mineralogical composition in these bentonites. It can be deduced from the study of the evolution of incompatible LILE and HFSE elements that the effect of temperature is to cause the fractionation of the incompatible elements, thus favouring the entry into a solid phase of elements with a small radius and high charge (HFSE) compared with those with a large ionic radius (LILE). The entry of both into the solid phase increases in the area of more alteration, that is, the contact area. In areas where temperature does not have any effect, such as CT-2 profile, it is possible to see that both groups of elements mobilise in the same way. Figs. 6 and 7 show the evolution of the concentrations of transition elements depending on distance for profiles CT-1 and CT-2, respectively. Fig. 6, corresponding to the thermal contact (CT-1) shows that the maxima in Sc, Cr, Cu, Co and Ni are in the first 400 cm. Pb shows two maxima, at 70 and 800 cm, respectively. A second axis of ordinates had been used for elements V and Ni in Fig. 7, corresponding to the contact for profile CT-2, where it can be observed that the most important fluctuations also occur near the contact. Although there is a maximum in Cr, Cu, Co, Pb and V in the sample at 800 cm, this maximum does not represent a profile trend and is considered as an isolated behaviour. Both figures again show that the most important fluctuations of the transition elements are located in areas near both contacts. Compatible elements are those which have varied their concentrations more intensely as a result of the proximity of a supergene alteration zone connected with a contact area. Figs. 8 and 9 show the concentrations of light (La-Eu) and heavy (Gd-Lu) (REE) for both profiles (CT-1 and CT-2). The parallel evolution of light and heavy REE shows that no fractionation occurs between them. Nevertheless, values for the thermal contact (profile CT-1) show a more marked mobilisation of REE than those produced in the contact for profile CT-2. The Coryell-Masuda diagrams for the profiles studied (Figs. 8 and 9) show that the proximity of a thermal contact area does not cause substantial changes in the distribution of the REE of the bentonite samples. This behaviour is similar to that of a typical model of sedimentary rocks (Chondrite-normalized REE diagrams for sediments and sedimentary rocks) (McLennan, 1989) although with less enrichment in La. Elements such as Eu and Ce have small variations compared with chondrite and andesite normalized patterns (Fig. 8a and b). The most marked
Fig. 3. Evolution of the LILE and HFSE elements depending on distance for profile CT-1 corresponding to the termal contact.
profiles normalized to chondrite (Evensen et al., 1978) (a), andesite (Taylor and McLennan, 1985) (b), and the RS (c).
3. Results and discussion Minor, trace and REE in the total sample are detailed in Table 2. Figs. 3 and 4 show a comparison of values of Light Elements Lithofile Elements (LILE) compared with High Field Strong Elements (HFSE) elements for both profiles. CT-1 profile in the first 400 cm (Fig. 3) shows that the LILE elements are at a minimum compared with the maximum of the HFSE. Sr presents a maximum value of 267 ppm at 220 cm from the contact, decreasing gradually until 150 ppm with distance. Rb has the highest concentrations near the contact, with values around 130 ppm, and gradually decreases with distance, showing average values of 75 ppm. For the CT-2 profile (Fig. 4), the first observation that can be made is that there is not a homogenous pattern of lithophile elements near the contact, as it occurred in profile CT-1. In profile CT-2 it is not possible to detect any fractionation of the lithophile elements near the contact. Barium shows anomalous behaviour with a very high maximum of 650 ppm at 800 cm, in comparison to with the average Ba value calculated for the entire outcrop (207 ppm). This highlights that Ba is sensitive to the alteration processes that have taken place in the profiles studied, in accordance with Christidis (1998) who found Ba to be relatively stable in the first stages of alteration, but to display a sudden increase in concentration in a more advanced stages. Nevertheless, temperature does not seem to be the only factor responsible for Ba 5
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Fig. 4. Evolution of the LILE (a) and HFSE (b) elements depending on distance for profile CT-2 corresponding to stratigraphical contact.
anomalies are observed in comparison with the RS (Figs. 8c and 9c). This would mean that the processes which caused those anomalies would have occurred after the formation process of bentonite. The negative anomaly in Ce observed in the samples near the contact areas could be indicative of the participation of seawater mobilised in favour of these surfaces (McLennan, 1989, 1999; Shikazono et al., 2008). On the other hand, Eu under reducing conditions behaves in a similar fashion to the calc-alkaline elements Ca and Sr, so it can replace both behaving in a less incompatible manner (Richardson and McSween, 1989). These values are characteristic of reducing conditions, which indicates that the bentonite process formation occurred in supergene conditions in this case. Shikazono et al. (2008) in studies about geochemical behaviour of rare elements in hydrothermal altered rocks, found a negative Eu anomaly as a result of leaching of Eu2 + by reducing hydrothermal solutions.
Fig. 5. Evolution of Rb (ppm) against oxygen stable isotope composition (smow).
6
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Fig. 6. Evolution of the transition elements Sc, Cr, Cu, Co, Ni, V, Zn and Pb depending on distance for profile CT-1 corresponding to thermal contact.
Fig. 8. The Coryell-Masuda diagrams for the profile CT-1 (thermal contact) normalized to chondrite (a), andesite (b) and reference simple (c). Legend shows distance (cm) from contact to samples.
Taking into account the above considerations, the profiles should follow a pattern that shows that the areas near the contact, where the rock has been in the presence of seawater (Ce/Ce* < 1) are also where the lowest values of Eu/Eu* should be measured. These premises are met in the case of profile CT-2 (Fig. 10b), except for the samples located at 800 and 1300 cm, where both the Ce/Ce* and Eu/Eu* values are abnormally high. The anomaly in Eu in these samples may be related to the high concentrations of Ba present (over 5000 ppm above average), since both elements have a similar ionic radius and identical coordination. Similar behaviour was reported by McLennan (1999), and Richardson and McSween (1989), who described the replacement of Eu by Sr and/or by Ca in the feldspar structure. According to Hurlbut and Klein (1991), high concentrations of Ba together with Pb, Cu, Co and Mn are associated with minerals such as hyalophane, manganese, barite, siderite, etc., in connection with a hydrothermal vein. These data correspond to high concentrations of Mg, Mn, Fe, Co, Pb, Cr, Cu and Mo present in the 800 cm sample, which significantly exceeded the deposit average concentration, and which could be connected with vein mineralisations, such as those described above. Therefore, it is feasible to believe that profile CT-2 crosses a small hydrothermal vein at around 800 cm away from the stratigraphic contact, which would explain the abnormally high concentrations of the various trace elements. According to McLennan (1999), Ce and Mn are intimately related. It is not, therefore, surprising that Ce is also enriched at 800 cm from the stratigraphical contact, where there are abnormally high concentrations
Fig. 7. Evolution of the transition elements Sc, Cr, Cu, Co, Ni, V, Zn and Pb depending on distance for profile CT-2 corresponding to the stratigraphical contact.
7
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Fig. 9. The Coryell-Masuda diagrams for the profile CT-2 (stratigraphical contact) normalized to chondrite (a), andesite (b) and reference simple (c). Legend shows distance (cm) from contact to samples.
Fig. 10. Evolution of the Ce/Ce* and Eu/Eu* relations versus distance (cm) for profile CT-1 corresponding to the termal contact (a) and for profile CT-2 corresponding to the estratigraphical contact (b).
8
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Fig. 11. Fractionation for heavy, intermediate and light REE versus distance from both contacts: a) Thermal contact (CT-1) and b) stratigraphical contact (CT-2). La/Lu relation is plotted in the secondary axis.
4. Conclusions
of Mn (several times above the average). In the case of profile CT-1 represented in Fig. 10a, it can be seen that two maxima occur in the Ce/Ce* relation at a distance of 70 and 300 cm from the thermal contact. The one at 70 cm coincides with the Mn maximum in the profile (analogue situation to that of profile CT-2) and the 300 cm maximum coincides with an area of accumulation, where smectite is being generated, and, therefore, where the various elements that have been mobilised in the areas near the contact are deposited. Fig. 11a and b shows that the fractionation between light rare earth elements (LREE) and heavy rare earth elements (HREE) has fluctuations in areas close to both types of contact. Fractionation occurs homogeneously, showing a parallel evolution between them, which is constant throughout the profile. Only the La/Nd relation has a behaviour different for the rest in the first 600 cm of contact. This is because the large ionic radius characteristic of LREE and their high charge make them the most incompatible in the entire group. They only form part of very open structures, such as those formed mainly by sedimentary minerals (McLennan, 1999). It can be seen from these graphs (Fig. 11) that, compared with the Sm/Dy and Ho/Lu relations, the La/Nd one increased in the areas that have suffered more alteration, favoured by the availability of fluids due to their closeness to the contact area. By contrast, in the areas where leaching of neoformed sedimentary minerals has occurred due to the circulation of fluids in the area close to the contact, the La/Nd relation decreased compared with the Sm/Dy and Ho/Lu relations. These fluid circulation areas are favoured by the presence of a thermal gradient (Fig. 11a). These observations concur with those made in the study of Eu/Eu* and Ce/Ce* relations. Therefore, the effect of temperature caused mobilisation of rare earth elements. This mobilisation became obvious when studying the behaviour of all the rare earth elements (∑ REE) with distance to the different contacts. The evolution of transition elements represented by Cu and V followed the same trend as that observed in rare earth elements. The availability of fluids near the contact area encourages the incorporation of these elements. This availability becomes more intense with temperature, which leads to more element enrichment (Table 2).
The study of trace elements and rare earth behaviour allowed to know the degree of the alteration in the bentonite. It has been shown that there are no major differences in the REE distribution of bentonite subjected to a thermal contact area in front of a stratigraphic contact zone. Also, there are no significant differences with the REE pattern of andesite obtained by Taylor and McLennan (1985). The differences found are consistent with the differences described for supergene alteration processes. These similarities in the patterns indicate that the processes of bentonitization and later alteration related to the contact in Cala del Tomate outcrop, do not involve a significant transformation in the pattern of rare earths. On the whole, the presence of a contact area causes element mobilisation. This mobilisation, depending on whether there is a temperature gradient, occurs more intensely and penetrates further into the bentonite, in other words, it leads to quantitative differences. On the other hand, there are elements whose behaviour depends directly on temperature, so they behave as qualitative indicators of its action in the system. Consequently, Rb mobilises significantly near a thermal contact, following a pattern that contrasts with its behaviour in a mechanical contact. Other elements that are sensitive to the effect of temperature are lithophile elements. These elements describe a fractionation of LILE compared with HFSE near the thermal contact. The main chemical differences between thermal contact and stratigraphic contact area are not subjected to the effect of temperature is the incorporation of trace elements with a small radius (HFSE) in the structure of the smectites subject to the effect of temperature, in detriment of those with a larger radius (LILE). It can be deduced from the study of the evolution of incompatible LILE and HFSE elements that the effect of the temperature that has acted on the bentonite mass causes the fractionation of the incompatible elements, thus favouring the entry into a solid phase of elements with a small radius and high charge (HFSE) compared with those with a large ionic radius (LILE). When temperature does not have any control, such as the case of profile CT-2, it is possible to see that 9
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both groups of elements mobilise in the same way. The entry of both into the solid phase increases in the area of more alteration, which, in this case, is the contact area. Acknowledgements The authors are grateful to A. Caballero for his graphical assistance. References Arslan, M., Abdioglu, E., Kadir, S., 2010. Mineralogy, geochemistry, and origin of bentonite in Upper Cretaceous pyroclastic units of the Tirebolu area, Giresun, Northeast Turkey. Clay Clay Miner. 58 (1), 120–141. Banfield, J.F., Eggleton, R.A., 1989. Apatite replacement and rare earth mobilization, fractionation and fixation during weathering. Clay Clay Miner. 38, 77–89. Caballero, E., 1985. Quimismo del proceso de bentonitización en la región volcánica de Cabo de Gata (Almería). Ph.D. thesis University of Granada, Spain (339 pp.). Caballero, E., Jiménez de Cisneros, C., Martinez, J.A., 2017. Thermal alteration in a bentonite from Cabo de Gata, Almería, SE Spain. Chem. Erde (in revision). Caggianelli, A., Fiore, S., Mongelli, G., Salvemini, A., 1992. REE distribution in the clay fraction of pelites from the southern Apennines, Italy. Chem. Geol. 99, 253–263. Christidis, G.E., 1998. Comparative study of the mobilityof major and trace elements during alteration of an andesite and a rhyolite to bentonite, in the islands of Milos and Kimolos, Aegean, Greece. Clay Clay Miner. 46 (4), 379–399. Coogan, L.A., Kempton, P.D., Saunders, A.D., Norry, M.J., 2000. Melt aggregation within the crust beneath the Mid-Atlantic Ridge: evidence from plagioclase and clynopyroxene major and trace element compositions. Earth Plan. Sci. Lett. 176, 245–257. Cullers, R.L., Chaudhuri, S., Kilbane, N., Koch, R., 1979. Rare earths in size fraction and sedimentary rocks of Pennsylvanian-Permian age from the mid-continent of the USA. Geochim. Cosmochim. Acta 43, 1285–1302. Evensen, N.M., Hamilton, P.J., O'Nions, R.K., 1978. Rare-earth abundances in chondritic meteorites. Geochim. Cosmochim. Acta 42, 1199–1212. Fernández Soler, J.M., 1992. El volcanismo calco-alcalino de Cabo de Gata (Almería). Ph.D. thesis University of Granada, Spain. Hurlbut, C.S.Jr., Klein, C., 1991. In: Reverté, S.A. (Ed.), Manual de mineralogía de Dana. Linares, J., Caballero, E., Reyes, E., Huertas, F., 1987. Trace element mobility in bentonite formation. In: Hurst, R.W., Davis, T.E., Augustithis, S.S. (Eds.), The Practical Applications of Trace Elements and Isotopes to Environmental Biogeochemistry and Mineral Resources Evaluation. Theophrastus Publication, S.A., pp. 233–250. Marks, M., Halama, R., Wenzel, T., Markl, Gregor, 2004. Trace element variations in clinopyroxene and amphibole from alkaline to peralkaline syenites and granites: implications for mineral-melt trace-element partitioning. Chem. Geol. 211, 185–215.
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