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Article

Geochemical Characteristics of Aluminum-Bearing Iron Ores: A Case Study from the Kolijan Karst-Type Bauxite Deposit, Northwestern Iran

by
Ali Abedini
1,* and
Maryam Khosravi
2
1
Department of Geology, Faculty of Sciences, Urmia University, Urmia 57561-51818, Iran
2
Department of Mining Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
*
Author to whom correspondence should be addressed.
Minerals 2024, 14(2), 151; https://doi.org/10.3390/min14020151
Submission received: 23 November 2023 / Revised: 18 January 2024 / Accepted: 28 January 2024 / Published: 30 January 2024
(This article belongs to the Section Mineral Deposits)
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Abstract

:
The Kolijan bauxite deposit (southeast Mahabad, northwestern Iran) mainly contains aluminum-bearing iron ores and was deposited in karstic depressions and sinkholes of the middle Permian carbonate rocks of the Ruteh Formation. Based on microscopic observations, the aluminum-bearing iron ores were allogenic in origin. According to XRD and SEM-EDS analyses, hematite and goethite are their main constituents, accompanied by lesser amounts of kaolinite, illite, amesite, boehmite, rutile, anatase, calcite, pyrolusite, crandallite, and parisite-(Ce). Chondrite-normalized REE patterns are indicative of fractionation and enrichment of LREE (La–Eu) compared to HREE (Gd–Lu), along with positive Eu and Ce anomalies (Eu/Eu* = 2.29–5.65; Ce/Ce* = 3.63–5.22). Positive Ce anomalies can be attributed to the role of carbonate bedrock as a geochemical barrier and the precipitation of parisite-(Ce). A strong positive correlation between Eu/Eu* and Ce/Ce* (r = 0.84) indicates that Eu anomalies, similar to Ce anomalies, are closely dependent on an alkaline pH. The distribution and fractionation of elements in the iron ores were controlled by a number of factors, including the pH of the environment in which they formed, wet climatic conditions, adsorption, isomorphic substitution, scavenging, co-precipitation, fluctuations of the groundwater table level, and the role of carbonate bedrock as a geochemical barrier. This research indicates that the aluminum-bearing iron ores were probably generated from the weathering of basaltic protolith.

1. Introduction

The term bauxite was first used by Berthier in 1821 referring to alumina-rich sediments in the Les Baux region of France. Bauxite deposits are formed by the weathering of aluminosilicate-rich rocks such as granite, basalt, diabase, andesite, nepheline syenite, marl, tuff, clayey limestone, shale, slate, etc., in tropical and subtropical regions under warm and humid climatic conditions [1]. Al (oxyhydr)oxides are the dominant mineral components of bauxite ore [1], together with variable amounts of Fe and Ti (oxyhydr)oxides. Bauxite deposits are classified into two main categories: (1) bauxite deposits on aluminosilicate bedrocks, and (2) those on carbonate bedrocks, known as karst-type bauxite deposits [1,2]. Studies conducted over the past two decades have shown that some karst bauxite deposits show a characteristic structure called “iron-bauxite”. This structure has been reported from the Nurra bauxite deposit in Italy [3], bauxite deposits in northwestern Iran [4,5], and most bauxite deposits in China [6,7,8,9,10]. In these deposits, the “bauxite” part of the structure includes bauxite ores, bauxitic clays, and clay-rich bauxites. The “iron-rich” part of the structure includes iron-rich clays, bauxitic iron ores, and aluminum-bearing iron ores [3,4,5,6,7,8,9,10].
In recent years, there have been studies of the distribution and fractionation of trace elements and rare earth elements (REE), and factors controlling their distribution and mobility in bauxite deposits worldwide. These studies show that the distribution and fractionation of trace elements and REE in bauxite deposits is controlled by a number of factors, including the chemical composition of the protolith and bedrocks [11,12,13], physicochemical conditions in the weathering environment (Eh–pH) [14,15,16], fluctuations of the water table [17,18], the presence of organic and inorganic ligands in the soil [19,20], bacterial activity, mineral species in bedrocks [21,22,23,24,25], adsorption, scavenging [3,26,27], climatic conditions [28,29,30,31], stability of REE-bearing primary and secondary minerals [6,32,33,34], chemical properties of elements during weathering [35,36], complexation with different ligands, and diagenetic and epigenetic processes [37,38,39].
Similarly, in recent years, comprehensive studies have been carried out on geodynamic evolution and geochemical characteristics of the Iranian karst-type bauxite deposits [5,6,40,41,42,43,44,45,46,47,48,49]. The Iranian bauxite deposits are a part of the Irano–Himalayan karst bauxite belt [5,41,42,43,44,45,46,47,48,49]. The sedimentary hiatus during the Permian caused the generation and development of bauxite deposits in Iran. In northwestern Iran, bauxite deposits dominantly occur in karstic sinkholes and depressions of middle–late Permian shallow carbonate bedrocks of the Ruteh and Nessen Formations. Based on geochemical investigations, these deposits probably related to the weathering of igneous rocks, mainly of a mafic composition [48,49]. Studies show that the middle–late Permian bauxite deposits in northwestern Iran mainly consist of bauxitic clays, bauxites, and Fe-rich bauxites [41,42,43,44,45,46,47,48,49]. Mineralogical and geochemical features of these categories of the northwestern Iran bauxite deposits were presented by Abedini and Khosravi [43] and Abedini et al. [5,45,46,47]. In addition, Al-bearing iron ores are developed in some bauxite deposits of the northwestern Iran, but mechanisms of the generation and development of the ores have not been considered.
The Kolijan bauxite deposit is one of the typical karst-type bauxite deposits in southeast Mahabad, northwestern Iran. The development of “iron-bauxite” structure is one of the most important geological features of this deposit. The Al-bearing iron ores were taken from the lowermost parts of the selected profile in the Kolijan area. The mineralogy and geochemistry of the Kolijan Al-bearing iron ores from the perspective signatures will clarify the mechanism of formation and development of this ore type and also help to explore potential resources of this ore type in the Irano-Himalayan karst-type bauxite belt. The main aims of this paper are to determine the factors controlling the distribution and fractionation of trace elements and REE, the reasons of Ce and Eu anomalies, the formation environment, and the protolith of the Kolijan Al-bearing iron ores.

2. Geological Setting of the Deposit

According to structural divisions of Iran proposed by Nabavi [50], the Kolijan area is a part of the Khoy–Mahabad structural zone (Figure 1). From the oldest to youngest, rock units in the Kolijan area include shale and phyllite of the Kahar Formation (Precambrian), shale and dolomite of the Soltanieh Formation (Cambrian), sandstone of the Lalun Formation (Cambrian), dolomite and limestone of the Mila Formation, dolomitic limestone of the Ruteh Formation (Permian), volcanic rocks, carbonates, along with phyllite and sandstone of Cretaceous age, limestone of the Qom Formation (Miocene), Plio-Quaternary alkaline volcanic lavas, and recent alluvial sediments (Figure 2).
The bauxite deposit in the Kolijan area is present in five discrete outcrops as stratiform layers and lenses in karstic sinkholes and depressions of the middle Permian dolomitic limestones of the Ruteh Formation (Figure 2). They have a length of 1.4 km and a variable thickness from 8 to 18 m with an overall trend of NE–SW and NW–SE. According to field observations, ores of these five layers and lenses have various colors, ranging from red, brownish red, brick red, through gray, to green, greenish cream, and white. The white, gray, green, and greenish cream ores are clay-rich bauxites (Figure 3a) and bauxitic clays (Figure 3b), and mainly occur in the upper parts of layers and lenses. Whereas, red, brownish red, and brick-red ores are Al-bearing iron ores and mainly occur in the lower parts of layers and lenses (Figure 3a,b and Figure 4a,b). Only the Al-bearing iron ores are considered in this study; they are massive with high specific gravity and hardness. The supergene oxidation on the surface, the presence of macropisoids, ooids, pisoids, and nodular forms, and traces of manganese dendrites are the significant mesoscopic characteristics of the Al-bearing iron ores.

3. Method of Investigation

Following field works, 11 whole-rock samples of the Al-bearing iron ores from the lower parts of the Kolijan deposit were taken. Petrographical and mineralogical studies of the collected samples were examined by Olympus (Tokyo, Japan) BX60F5 Transmitted and Reflected Light Microscope at the Department of Geology of Urmia University, Iran and X-ray diffraction (XRD) with a D-5000 (Munich, Germany) SIMENS diffractometer at the Kansaran Binaloud Co., Tehran, Iran. Mineralogical results of the Kolijan Al-bearing iron ores are presented in Table 1. Microscale mineralogical analysis of the samples was performed at the Razi Metallurgical Research Center, Iran by scanning electron microscope coupled with energy-dispersive X-ray spectrometry (SEM–EDS) using a Hitachi (Tokyo, Japan) S-3400 N SEM equipped with a Link Analytical Oxford IE 350 energy dispersive X-ray spectrometer (EDS) under the following conditions: 15 kV, 1 nA-beam current, and 1 μm-beam diameter.
Major oxides and trace elements, including REE, contents of 11 samples from the Kolijan Al-bearing iron ores were measured at the ALS Chemex Laboratory, Canada by inductively coupled plasma–atomic emission spectrometry (ICP–AES) and inductively coupled plasma–mass spectrometry (ICP–MS), respectively. Results of geochemical analyses of major oxides and trace elements of the studied ores, southeast Mahabad, northwestern Iran are presented in Table 2. About 0.2 g of the powdered samples were mixed with lithium tetraborate–lithium metaborate flux, fused in a furnace at 1000 °C, and then cooled, digested with nitric acid, and finally diluted to 100 mL. Values of loss-on-ignition (LOI) were obtained by weight difference after ignition at 1000 °C in a muffle furnace. The detection limit for major oxides was 0.01 wt%, for trace elements from 0.05 to 10 ppm, and for REE from 0.01 to 0.5 ppm. In this paper, Pearson correlation coefficients among the elements were calculated by the SPSS statistics software (version 16).

4. Results and Discussion

4.1. Texture and Mineralogy of the Al-Bearing Iron Ores

Textural components in the Kolijan Al-bearing iron ores include concentric shapes, such as micro-ooids, ooids, pisoids, and macropisoids, secondary films and coatings, nodules, concretions, clasts (clastic fragments), and fissure fillings (Figure 5a–c). In polished sections, hematite is the only mineral identified in the core of ooids, pisoids (Figure 5b), spastoids, and macropisoids. The concentric forms are sometimes elliptical, due to effects of tectonic pressures (Figure 5d). Hematite in the studied ores occurs in the form of nodule, granule, sphere, oval, and veinlet. The nodules, ranging from 3 to 9 mm in size, are almost spherical to oval-shaped and sometimes show weak orientations in the matrix of the Al-bearing iron ores. Ooidic, pisoidic, nodular, pelitomorphic, collomorphic, clastic, and round-grained textures are the most dominant textures identified in the Kolijan Al-bearing iron ores. Micro-ooids and ooids are sometimes observed in the core of pisoids (Figure 5a), indicating a multi-cyclic nature of the formation environment for the Al-bearing iron ores [51]. Moreover, irregular or radial fractures in hematite cores of concretionary forms (Figure 3b) are probably related to gel shrinkage during the formation and development of the ores [1]. According to Bárdossy [1], the presence of a round-grained texture (Figure 5c) is indicative of an allogenic origin for the Kolijan Al-bearing iron ores. Elongation of texture-forming components and elongated ooids with a hematite core are related to the function of tectonic processes and the effect of overburden pressures on the ores (Figure 5d). The secondary coatings around the hematite are possibly formed during diagenetic or epigenetic processes (Figure 5e) [2]. In any case, the presence of fractured pisoids and clastic fragments mainly of hematite suggests an allogenic origin for the Kolijan Al-bearing iron ores (Figure 5f).
The presence of Fe-bearing nodules in the studied samples suggests that fluctuations of the groundwater table level played a role in the development and evolution of the Kolijan Al-bearing iron ores. According to Valeton [52], fluctuations of the water-table level produce Fe-bearing nodules in weathered deposits. As a whole, it can be deduced that the development and evolution of the studied ores is related to the chemistry of the groundwater. In other words, the dissolution of carbonate bedrocks, promoting a higher pH of weathering solutions, can cause precipitation of Fe in the Kolijan area [33,41].
XRD analyses show that hematite and goethite are the main constituents of the Kolijan iron ores, accompanied by lesser amounts of kaolinite, illite, boehmite, calcite, rutile, anatase, amesite, pyrolusite, and crandallite (Table 1, Figure 6). Hematite and goethite as the main mineral phases, with kaolinite as an accessory mineral, are present in all the studied samples. Pyrolusite in six samples, rutile and crandallite in five samples, calcite and amesite in four samples, and boehmite, anatase, and illite in two samples were identified as accessory minerals (Table 1). According to SEM–EDS analyses, parisite-(Ce) occurs as individual subhedral crystals on hematite and kaolinite (Figure 7a,b). This mineral has been reported from other karst-type bauxite deposits, such as Wuchuan–Zheng’an–Daozhen, Quyang, Taiping, Guangxi, and Wulong–Nanchuan bauxite deposits in China [27,29,53,54,55], Abruzzi and Apulian bauxite deposits in Italy [30,32,35], Parnassos–Ghiona bauxite deposit in Greece [25], and Soleiman Kandi, Baghoushi, Bidgol, and Tang-e-Pirzal bauxite deposits in Iran [41,46].
Minerals 14 00151 g005
Figure 5. Photomicrographs showing textural and mineralogical features of the Kolijan Al-bearing iron ores. (a) Micro-ooids and ooids in the core of a pisoid, indicating the multi-cyclic nature of the formation environment. (b) Concretion forms with a hematite core, which have irregular fractures, due to gel shrinkage. (c) Round-grained texture. (d) Elongation and orientation in concretion forms. (e) Oval-shaped ooids with a hematite core. (f) Fractured clasts and pisoids. All figures are in reflected light/cross polarized light (XPL). Hem = hematite [56].
Figure 5. Photomicrographs showing textural and mineralogical features of the Kolijan Al-bearing iron ores. (a) Micro-ooids and ooids in the core of a pisoid, indicating the multi-cyclic nature of the formation environment. (b) Concretion forms with a hematite core, which have irregular fractures, due to gel shrinkage. (c) Round-grained texture. (d) Elongation and orientation in concretion forms. (e) Oval-shaped ooids with a hematite core. (f) Fractured clasts and pisoids. All figures are in reflected light/cross polarized light (XPL). Hem = hematite [56].
Minerals 14 00151 g005

4.2. Distribution of Major Elements in Kolijan Iron Ore

Among major oxides, Fe2O3 is the main constituent of the Kolijan iron ores, and occurs in the range 60.90–91.12 wt% (average = 82.88 wt%). The next most abundant components of the studied ores are SiO2 (1.47–14.42 wt%, average 4.08 wt%) and Al2O3 (0.27–8.12 wt%, average 1.97 wt%) (Table 2). Major oxides TiO2 (0.08–2.65 wt%, average 0.71 wt%), P2O5 (0.21–1.35 wt%, average 0.71 wt%), and MnO (0.41–1.09 wt%, average 0.75 wt%) occur at significantly lower levels. Alkaline and alkaline earth oxides (Na2O, K2O, MgO, and CaO) are in the range 0.01 to 1.97 wt%.
There is a strong negative correlation between Al2O3 and Fe2O3 in the Kolijan iron ores (r = −0.99, p < 0.01; Figure 8a). This strong negative correlation is indicative of the different geochemical behavior of Al and Fe during weathering processes related to Eh−pH changes of groundwater during weathering [11,57]. Recent studies indicate that the competition between Al and Fe in the generation of Al and Fe (oxyhydr)oxides during weathering depends on climatic changes. Iron concentration occurs under wetter climatic conditions than Al concentration, which is favored under arid climatic conditions [33]. The significant concentration of Fe2O3 compared to Al2O3 in the studied ores suggests that climatic conditions were probably wet during the formation of the iron ores. Moderate-to-strong negative correlations between Fe2O3 and SiO2 (r = −0.98, p < 0.01; Figure 8b), MgO (r = −0.95, p < 0.01; Figure 8c), TiO2 (r = −0.97, p < 0.01; Figure 8d), MnO (r = −0.83, p < 0.01; Figure 8e), and P2O5 (r = −0.74, p < 0.01; Figure 8f) are the also observed, indicating that the amount of kaolinite, boehmite, crandallite, pyrolusite, rutile, anatase, and amesite decreases with increasing amounts of hematite and goethite. A strong positive correlation between Al2O3 and TiO2 (r = 0.96, p < 0.01) indicates the similar behavior of these elements during weathering [58,59]. The Al2O3–SiO2–Fe2O3 ternary diagram of Schellmann [60] indicates that the Kolijan iron ores formed during strong laterization (Figure 9). This diagram also shows that during the formation and development of the studied ores, the content of Fe increased and the content of Si and Al decreased.

4.3. Distribution of Trace Elements in Kolijan Iron Ore

Cr is the most abundant trace elements, ranging from 470 to 1010 ppm, average 851.8 ppm. Barium (63–286.1 ppm, average 160.4 ppm), V (80–312 ppm, average 133.8 ppm), Sr (76.3–265.4 ppm, average 156.8 ppm), Pb (46–152 ppm, average 91.1 ppm), Ni (42–109 ppm, average 82.6 ppm), Co (14.6–32.1 ppm, average 27.8 ppm), Zr (4–71 ppm, average 17.4 ppm), and U (5.6–18.2 ppm, average 9.1 ppm) are the next most abundant trace elements of the studied ores. Average values for Th, Hf, Nb, Cs, Rb, Ga, Y, and Ta are less than 4 ppm.
Strong positive correlations between Fe2O3 and Cr (r = 0.89, p < 0.01), Co (r = 0.87, p < 0.01), and Ni (r = 0.91, p < 0.01) indicate that trace elements Cr, Co, and Ni were incorporated into Fe (oxyhydr)oxides by scavenging and/or co-precipitation [61,62,63,64,65,66]. Moderate-to-strong positive correlations between K2O and Ba (r = 0.72, p < 0.01), Cs (r = 0.93, p < 0.01), and Rb (r = 0.96, p < 0.01) indicate that trace elements Ba, Cs, and Rb are easily incorporated into the mineral structure of clay minerals, such as illite, as interlayer cations [67,68,69,70]. Moreover, a strong positive correlation between CaO and Sr (r = 0.92, p < 0.01) suggests that Sr in the iron ore is probably controlled by calcite.
Strong positive correlations between Pb and MnO (r = 0.95, p < 0.01) and Al2O3 (r = 0.80, p < 0.01) indicate that scavenging of Pb by Mn oxides, along with the substitution of Pb for Al in boehmite and/or the adsorption onto surfaces of this mineral probably were responsible for the distribution and concentration of Pb in the ores, as outlined by Mordberg [21]. Similarly, a strong positive correlation between Al2O3 and Zr (r = 0.99, p < 0.01) indicates the distribution and concentration of Zr in the mineral structure of boehmite as adsorption and/or isomorphic admixture [21]. Strong positive correlations between Al2O3, SiO2, and TiO2, and trace elements U, Th, Hf, Nb, Ga, Y, and Ta (r ≥ 0.91, p < 0.01) indicate the role of clays, boehmite, and rutile/anatase in the distribution of these trace elements.
Table 2. Major, trace, and rare earth elements contents of the Kolijan iron ore. (La/Yb)N = (La/LaN)/(Yb/YbN); (∑LREE/∑HREE)N = (∑LREE/∑LREEN)/(∑HREE/∑HREEN); Eu/Eu* = (Eu/EuN)/√[(Sm/SmN) × (Gd/GdN)]; Ce/Ce* = (Ce/CeN)/√[(La/LaN) × (Pr/PrN)]. The subscript “N” refers to chondrite normalized values [71].
Table 2. Major, trace, and rare earth elements contents of the Kolijan iron ore. (La/Yb)N = (La/LaN)/(Yb/YbN); (∑LREE/∑HREE)N = (∑LREE/∑LREEN)/(∑HREE/∑HREEN); Eu/Eu* = (Eu/EuN)/√[(Sm/SmN) × (Gd/GdN)]; Ce/Ce* = (Ce/CeN)/√[(La/LaN) × (Pr/PrN)]. The subscript “N” refers to chondrite normalized values [71].
Detection LimitKj-01Kj-02Kj-03Kj-04Kj-05Kj-06Kj-07Kj-08Kj-09Kj-10Kj-11
SiO2 (wt%)0.013.721.671.852.811.471.882.334.688.1514.421.88
Al2O30.011.680.320.361.020.270.740.752.714.628.121.11
Fe2O30.0182.9989.9388.7485.8791.1286.8188.1479.4572.8960.984.87
CaO0.011.970.220.261.120.181.070.330.661.120.361.88
Na2O0.010.030.010.010.020.010.010.010.020.020.020.01
MgO0.010.230.180.220.230.130.20.140.220.540.910.17
K2O0.010.050.010.010.030.010.090.060.190.090.190.32
TiO20.010.640.080.080.410.080.250.081.611.572.650.41
MnO0.010.710.520.620.670.410.770.591.020.961.090.91
P2O50.010.610.260.310.310.210.920.321.021.351.231.22
L.O.I0.017.356.777.527.456.037.217.218.358.6510.027.16
Sum–99.9899.9799.9899.9499.9299.9599.9699.9399.9699.9199.94
U (ppm)0.058.246.696.115.676.288.757.059.613.8218.2610.39
Th0.050.780.100.120.440.110.340.191.072.434.270.58
Ba0.5214.479.596.1155.263191.1140.6215.3203.2120.3286.1
Hf0.22.10.50.81.40.20.81.23.13.76.60.8
Cr101010940920980910880960870580470850
Co0.526.329.428.627.330.331.632.127.124.514.634.5
Nb0.21.60.70.71.10.70.90.73.93.66.21.1
Cs0.010.290.130.050.170.050.180.160.680.510.510.82
Rb0.21.30.30.21.00.60.90.62.41.62.63.6
V514999105127938010213818331284
Ga0.15.03.23.34.13.23.22.63.45.27.53.0
Sr0.1227.9102.1124.8176.479.3195.1133.1173.8170.876.3265.4
Y0.51.60.60.71.10.62.12.31.23.89.71.8
Ta0.10.10.10.10.10.10.10.10.20.30.60.1
Zr21144847724417110
Pb5717474704610965124116152110
Ni5711029578109928379704288
La (ppm)0.56.11.72.64.40.94.92.312.510.914.67.3
Ce0.542.316.519.632.57.149.821.394.394.299.674.2
Pr0.031.250.330.490.870.171.610.842.472.752.782.72
Nd0.14.11.31.52.81.17.35.610.712.511.813.1
Sm0.031.180.240.330.760.152.541.811.863.371.984.75
Eu0.031.620.451.281.950.267.482.752.027.673.007.77
Gd0.051.570.450.601.090.294.812.371.145.962.99.01
Tb0.010.200.050.070.140.040.730.320.290.930.471.39
Dy0.051.320.470.570.950.364.201.981.565.653.457.84
Ho0.010.200.110.150.170.070.800.310.341.020.581.46
Er0.030.440.240.350.390.131.510.990.902.231.792.67
Tm0.010.090.020.020.050.030.160.100.140.280.240.31
Yb0.030.430.190.240.330.150.840.570.731.391.341.45
Lu0.010.110.020.020.060.020.120.120.120.240.260.22
∑LREE (La–Eu) (ppm)–56.5520.5225.8043.289.6873.6334.6123.85131.39133.76109.84
∑HREE (Gd–Lu) (ppm)–4.361.552.023.181.0913.176.765.2217.7011.0324.35
∑REE (La–Lu) (ppm)–60.9122.0727.8246.4610.7786.841.36129.07149.09144.79134.19
(La/Yb)N–1.050.660.800.990.440.430.301.270.580.810.37
(∑LREE/∑HREE)N–7.297.457.187.654.993.142.8813.344.186.822.54
Eu/Eu*–3.644.258.876.553.826.534.064.245.233.833.63
Ce/Ce*–0.933.495.023.963.794.144.043.493.873.923.57
La/Y–3.812.833.714.001.502.331.0010.422.871.514.06

4.4. Distribution Patterns of REE in Kolijan Al-Bearing Iron Ores

Contents of ∑LREE (La–Eu), ∑HREE (Gd–Lu), and ∑REE (La–Lu) in the Kolijan iron ores are in the range 9.68–133.76 ppm ∑LREE (average 69.35 ppm), 1.09–24.35 ppm ∑HREE (average 8.22 ppm), and 10.77–149.09 ppm ∑REE (average 77.57 ppm; Table 2). The (La/Yb)N and (∑LREE/∑HREE)N ratios indicate fractionation of LREE from HREE and have been used both in metallic and non-metallic deposits, and especially in karst bauxite deposits [33,48]. The fractionation of LREE from HREE depends on the pH of the depositional environment and mainly occurs as pH increases [33]. Under these circumstances, the HREE dissolve more readily in acid conditions, and so deposit as pH rises [33]. The (La/Yb)N and (∑LREE/∑HREE)N ratios in the Kolijan iron ore are in the range 0.30–1.27, average 0.70, and 2.54–13.34, average 6.13, respectively. Therefore, it suggests that changes in the pH of solutions responsible for weathering was the main agent of fractionation of LREE from HREE in the Kolijan iron ores.
The chondrite-normalized REE distribution diagram has been used to investigate fractionation of LREE from HREE in bauxites [33]. During weathering processes, mobility and concentration of REE is mainly controlled by the Eh and pH of the depositional environment [34,44]. Among REE, Ce behaves differently, due to its low ionization potential and atypical redox chemistry. As a result, the distribution of Ce anomalism has been widely used to track paleo-redox changes during generation of bauxite ores [33,41,44]. In the chondrite-normalized REE distribution diagram, the Kolijan iron ores are characterized by weak enrichment of LREE compared to HREE, together with significant positive Ce and Eu anomalies (Figure 10). The chondrite-normalized REE distribution in the ores indicates that changes in the oxidation potential and pH of the deposition environment were the dominant controls on the distribution and fractionation of REE [42].

4.5. Mineralogical Controls on REE Distribution in the Kolijan Al-Bearing Iron Ores

Correlation coefficients between REE and major oxides provide insights into the role of minerals in the distribution and concentration of lanthanides in the Kolijan Al-bearing iron ores. Moderate positive correlations of SiO2–LREE (r = 0.71, p < 0.01; Figure 11a) and Al2O3–LREE (r = 0.77, p < 0.01; Figure 11b) probably indicate the role of kaolinite and boehmite in the distribution and concentration of LREE through preferential adsorption and isomorphic substitution processes. In contrast, a weak positive correlation between Al2O3 and HREE (r = 0.33, p < 0.01; Figure 11c) indicates that kaolinite and boehmite did not exert a strong control on the distribution and concentration of HREE in the ores.
Weak-to-strong negative correlations between Fe2O3 and LREE (r = −0.82, p < 0.01; Figure 11d) and HREE (r = −0.38, p < 0.01; Figure 11e) show that hematite and goethite, as the main constituents of the Kolijan ores, probably did not exert a strong control on the distribution and concentration of both LREE and HREE in the ores. A strong positive correlation between K2O and LREE (r = 0.80, p < 0.01; Figure 11f) suggests that illite as an accessory mineral of the ores probably played an important role in the distribution and concentration of LREE in the ores. Similarly, a strong positive correlation between TiO2 and LREE (r = 0.85, p < 0.01; Figure 11g) suggests a pronounced role for rutile and anatase in the distribution and concentration of LREE in the ores. Moreover, moderate-to-strong positive correlations of MnO–LREE (r = 0.98, p < 0.01; Figure 11h), MnO–HREE (r = 0.63, p < 0.01; Figure 11i), P2O5–LREE (r = 0.96, p < 0.01; Figure 11j), and P2O5–HREE (r = 0.82, p < 0.01; Figure 11k) suggest that pyrolusite and crandallite probably acted as host minerals for both LREE and HREE in the Kolijan Al-bearing iron ores, respectively, possibly through adsorption and substitution processes.
On the whole, pyrolusite and crandallite were host minerals of both LREE and HREE in the ores, whereas boehmite, illite, kaolinite, rutile, and anatase only acted as host minerals for LREE. Indeed, fractionation and concentration of LREE from HREE in the ores can be attributed to mineral control. Adsorption by clay minerals, together with isomorphic substitution in boehmite and fixation in rutile and anatase play fundamental roles in the concentration of LREE, whereas fixation by phosphate minerals and scavenging by Mn oxides influenced the distribution and concentration of both LREE and HREE.

4.6. Ce and Eu Anomalies in the Kolijan Al-Bearing Iron Ores

In this study, Ce and Eu anomalies in the iron ores were calculated by the following formula:
Ce/Ce* = CeN/[(LaN × PrN)]0.5
Eu/Eu* = EuN/[(SmN × GdN)]0.5
The subscript “N” refers to values normalized to chondrite [71]. The Ce and Eu anomalies in the Kolijan iron ores are in the range 3.63–5.22 and 2.29–5.65, respectively. Various reasons for positive Ce anomalies in bauxite deposits have been presented in the literature. In general, positive Ce anomalies in ores in the upper parts of the weathered profile are attributed to oxidation of Ce3+ to less mobile Ce4+ and the precipitation of cerianite (CeO2) [25,27,30,72,73,74,75] and/or the precipitation of monazite-(Ce) during early diagenesis processes [44]. In contrast, positive Ce anomalies in ores in the lower parts of the weathered profiles result from the mobilization of Ce and the precipitation of Ce-rich fluorocarbonates, such as parisite-(Ce) [30]. Precipitation of parisite-(Ce) occurs as a result of the deposition of Ce3+ in an alkaline pH [26,76,77]. Wang et al. [27] stated that the reaction between fluoride complexes (CeF2+ or CeCO3F0) and Ca2+ and HCO3– causes the precipitation of parisite-(Ce) in bauxite ores. Therefore, positive Ce anomalies in the Kolijan Al-bearing iron ores can be attributed to the precipitation of parisite-(Ce), as identified by SEM–EDS analyses (Figure 7). This mechanism has been proposed for positive Ce anomalies in the lower parts of studied profiles from Wuchuan–Zhengan–Daozhen bauxite deposits, northern Guizhou, China) [27]. Because under alkaline conditions solutions rich in Ce3+ precipitate parisite in bauxite ores, it suggests that the pH of fluids involved in weathering had an important role in producing the strong positive Ce anomalies in Kolijan iron ores.
The behavior of REE in lateritic iron ores depends on the physicochemical conditions (Eh and pH) of the environment during the weathering processes that produced them [78]. In general, the leaching and precipitation of REE occurs in low and high pH environments, respectively [72,79]. In this study, alkaline conditions during the development of the aluminum-bearing iron ores is confirmed by the La/Y ratio and bivariate plot of La/Y versus REE (Figure 12). According to Crnički and Jurković [80], La/Y ratios more than 1 and less than 1 represent alkaline and acidic conditions, respectively. The La/Y ratio In the Kolijan Al-bearing iron ores is in the range of 1.00 to 10.42 (average 3.46), indicating buffering of weathering solutions by carbonate bedrocks during development of the ores. Strong positive Eu anomalies in the ores indicate alkaline conditions during ore formation. This supported by the plot of the studied ore samples on the Eu/Eu* vs. Ce/Ce* diagram. A strong positive correlation between Eu/Eu* and Ce/Ce* (r = 0.84, p < 0.01; Figure 13) suggests that, similar to positive Ce anomalies, strong positive Eu anomalies are produced by environmental conditions related to the role of carbonate bedrock as a geochemical barrier, as stated by Li et al. [53] and Wang et al. [55].

4.7. Protolith of the Kolijan Al-Bearing Iron Ores

In this study, various geochemical techniques such as accumulation coefficients of trace elements and contents of elements Cr and Ni, were used to determine the protolith(s) of the Kolijan Al-bearing iron ores. The following equation was utilized to calculate the accumulation coefficient of elements Mn, Th, Ba, Cr, Nb, V, Pb, and Ni [81]:
R = Σn (i = 1) Ki/Kl
where R is the accumulation coefficient of the element, i = the given element, n = the number of used elements, Ki = the average concentration of element i in the ores, and Kl = the average concentration of element i in the lithosphere [82].
The R values alone cannot determine the lithology of the protolith(s), so they are normalized to element Cr [83]. The bivariate plot of R versus Cr [83] reveals that the Kolijan iron ores plot in the area of influence of mafic precursor rocks (Figure 14). The bivariate plot of Log Cr versus Log Ni [84] also shows that the ores plot close to basaltic protolith (Figure 15). These findings are consistent with results from other karst-type bauxite deposits of different ages in northwestern Iran [41,42,43,44,45,46,47,48,49,85].

5. Conclusions

The most important results of the mineralogical and geochemical studies of the Kolijan Al-bearing iron ores, southeast Mahabad, northwestern Iran, are:
  • Microscopic observations show that the ores developed in multiple stages, and diagenetic and epigenetic processes were important during their formation.
  • Hematite and goethite are the main constituents of the Kolijan iron ores, accompanied by lesser amounts of kaolinite, illite, amesite, boehmite, rutile, anatase, calcite, pyrolusite, crandallite, and parisite-(Ce).
  • The distribution of trace elements in the Al-bearing iron ores developed by scavenging, co-precipitation, isomorphic substitution, adsorption, and fixation in new mineral phases, such as parisite-(Ce).
  • Preferential adsorption of LREE by kaolinite, illite, boehmite, rutile, and anatase resulted in their separation from HREE in the ores; pyrolusite and crandallite host both LREE and HREE in the ores.
  • Geochemical ratios, such as La/Y, indicate that fluctuations in the level of the water- table, and the function of carbonate bedrocks as a geochemical barrier caused fractionation and the concentration of REE during formation of the iron ores.
  • Strong positive Ce anomalies in the Kolijan iron ores result from alkalinity produced by carbonate bedrocks resulting in precipitation of parisite-(Ce).
  • Strong positive Eu anomalies in the ores are closely dependent on alkaline pH.
  • Based on geochemical data (Ni and Cr contents and accumulation coefficients of elements), basaltic rocks are the probable protolith of the Kolijan iron ores.

Author Contributions

Conceptualization, A.A.; methodology, A.A. and M.K.; software, A.A. and M.K.; validation, A.A. and M.K.; formal analysis, M.K.; investigation, M.K.; resources, A.A.; data curation, A.A.; writing—original draft preparation, A.A. and M.K.; writing—review and editing, A.A. and M.K.; visualization, A.A. and M.K.; supervision, A.A.; project administration, A.A.; funding acquisition, A.A. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially fully supported by the Bureau of Deputy of Research and Complementary Education of Urmia University.

Data Availability Statement

Data are contained within the article.

Acknowledgments

We extend our gratitude to Academic Editor of the Journal of Minerals for his editorial handling and four anonymous reviewers for reviewing and making critical comments on this manuscript. The authors thank Noel White of the University of Tasmania, Australia for English editing of the final version of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Map of structural zones of Iran [50] showing the location of the Kolijan area, southeast Mahabad, northwestern Iran.
Figure 1. Map of structural zones of Iran [50] showing the location of the Kolijan area, southeast Mahabad, northwestern Iran.
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Figure 2. Geological map of the study area showing the local geological setting and lithological units of the Kolijan deposit.
Figure 2. Geological map of the study area showing the local geological setting and lithological units of the Kolijan deposit.
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Figure 3. Photographs representing outcrops of the Al-bearing iron ores and their relationships with clay-rich bauxites (a) and bauxitic clays (b) in the Kolijan deposit, northwestern Iran.
Figure 3. Photographs representing outcrops of the Al-bearing iron ores and their relationships with clay-rich bauxites (a) and bauxitic clays (b) in the Kolijan deposit, northwestern Iran.
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Figure 4. Photographs showing outcrops of the Al-bearing iron ores (a,b) in the Kolijan deposit, northwestern Iran.
Figure 4. Photographs showing outcrops of the Al-bearing iron ores (a,b) in the Kolijan deposit, northwestern Iran.
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Figure 6. XRD patterns of the Kolijan Al-bearing iron ores. Abbreviations: Bhm = boehmite, Cal = calcite, Cran = crandallite, Gth = goethite, Hem = hematite, Kln = kaolinite, Pyro = pyrolusite, Rt = rutile [56].
Figure 6. XRD patterns of the Kolijan Al-bearing iron ores. Abbreviations: Bhm = boehmite, Cal = calcite, Cran = crandallite, Gth = goethite, Hem = hematite, Kln = kaolinite, Pyro = pyrolusite, Rt = rutile [56].
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Figure 7. SEM–EDS analyses of the Kolijan Al-bearing iron ores. (a) Parisite-(Ce) on hematite (a) and kaolinite (b) in sample Kj-09. Abbreviations: Hem = hematite, Kln = kaolinite, Par = parisite [56].
Figure 7. SEM–EDS analyses of the Kolijan Al-bearing iron ores. (a) Parisite-(Ce) on hematite (a) and kaolinite (b) in sample Kj-09. Abbreviations: Hem = hematite, Kln = kaolinite, Par = parisite [56].
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Figure 8. Bivariate plots of (a) Fe2O3–Al2O3, (b) Fe2O3–SiO2, (c) Fe2O3–MgO, (d) Fe2O3–TiO2, (e) Fe2O3–MnO, and (f) Fe2O3–P2O5 for the Kolijan iron ores, showing negative correlations between Fe2O3 and major oxides.
Figure 8. Bivariate plots of (a) Fe2O3–Al2O3, (b) Fe2O3–SiO2, (c) Fe2O3–MgO, (d) Fe2O3–TiO2, (e) Fe2O3–MnO, and (f) Fe2O3–P2O5 for the Kolijan iron ores, showing negative correlations between Fe2O3 and major oxides.
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Figure 9. Plot of the Kolijan iron ores on a SiO2–Al2O3–Fe2O3 ternary diagram [60].
Figure 9. Plot of the Kolijan iron ores on a SiO2–Al2O3–Fe2O3 ternary diagram [60].
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Figure 10. Chondrite-normalized REE patterns for the Kolijan iron ores. Data for the chondrite are from Taylor and McLennan [71].
Figure 10. Chondrite-normalized REE patterns for the Kolijan iron ores. Data for the chondrite are from Taylor and McLennan [71].
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Figure 11. Bivariate diagrams (a) SiO2–LREE, (b) Al2O3–LREE, (c) Al2O3–HREE, (d) Fe2O3–LREE, (e) Fe2O3–HREE, (f) K2O–LREE, (g) TiO2–LREE, (h) MnO–LREE, (i) MnO–HREE, (j) P2O5–LREE, and (k) P2O5–HREE for the Kolijan iron ores.
Figure 11. Bivariate diagrams (a) SiO2–LREE, (b) Al2O3–LREE, (c) Al2O3–HREE, (d) Fe2O3–LREE, (e) Fe2O3–HREE, (f) K2O–LREE, (g) TiO2–LREE, (h) MnO–LREE, (i) MnO–HREE, (j) P2O5–LREE, and (k) P2O5–HREE for the Kolijan iron ores.
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Figure 12. Bivariate plot of La/Y versus REE for the Kolijan Al-bearing iron ores, indicating an alkaline environment during formation of the ores.
Figure 12. Bivariate plot of La/Y versus REE for the Kolijan Al-bearing iron ores, indicating an alkaline environment during formation of the ores.
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Figure 13. Bivariate plot of Eu/Eu* versus Ce/Ce* for the Kolijan Al-bearing iron ores.
Figure 13. Bivariate plot of Eu/Eu* versus Ce/Ce* for the Kolijan Al-bearing iron ores.
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Figure 14. Log Cr versus R along with the influence area of various precursor rocks [83]. A, B, and C represent laterites from amphibolite, basalt, and granite precursor rocks, respectively. The numbers I, II, III, and IV denote the area of influence of ultramafic, mafic, intermediate (or argillaceous), and acidic precursor rocks, respectively. The Kolijan Al-bearing iron ores plot in the area of influence of mafic precursor rocks.
Figure 14. Log Cr versus R along with the influence area of various precursor rocks [83]. A, B, and C represent laterites from amphibolite, basalt, and granite precursor rocks, respectively. The numbers I, II, III, and IV denote the area of influence of ultramafic, mafic, intermediate (or argillaceous), and acidic precursor rocks, respectively. The Kolijan Al-bearing iron ores plot in the area of influence of mafic precursor rocks.
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Figure 15. Bivariate plot showing concentration of Cr versus Ni in laterite- and karst-type bauxite deposits with different protoliths [84]. Circles show data from the Kolijan iron ores.
Figure 15. Bivariate plot showing concentration of Cr versus Ni in laterite- and karst-type bauxite deposits with different protoliths [84]. Circles show data from the Kolijan iron ores.
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Table 1. Results of mineralogical analysis of the Al-bearing iron ores.
Table 1. Results of mineralogical analysis of the Al-bearing iron ores.
Kj-01Kj-02Kj-03Kj-04Kj-05Kj-06Kj-07Kj-08Kj-09Kj-10Kj-11
Hematite××××××××××××××××××××××××××××××××××××××××××××××××××
Goethite××××××××××××××××××
Kaoliniteacacacacacac××××ac
Calciteac acac ac
Pyrolusiteac ac acacacac
Anatase ac ac
Rutile ac acacacac
Crandallite ac acacacac
Illite ac ac
Amesite ac ac ac ac
Boehmite ac ac
ac: accessory; ×: the relative abundance of mineral.
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Abedini, A.; Khosravi, M. Geochemical Characteristics of Aluminum-Bearing Iron Ores: A Case Study from the Kolijan Karst-Type Bauxite Deposit, Northwestern Iran. Minerals 2024, 14, 151. https://doi.org/10.3390/min14020151

AMA Style

Abedini A, Khosravi M. Geochemical Characteristics of Aluminum-Bearing Iron Ores: A Case Study from the Kolijan Karst-Type Bauxite Deposit, Northwestern Iran. Minerals. 2024; 14(2):151. https://doi.org/10.3390/min14020151

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Abedini, Ali, and Maryam Khosravi. 2024. "Geochemical Characteristics of Aluminum-Bearing Iron Ores: A Case Study from the Kolijan Karst-Type Bauxite Deposit, Northwestern Iran" Minerals 14, no. 2: 151. https://doi.org/10.3390/min14020151

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