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Article

REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, 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 8415683111, Iran
*
Author to whom correspondence should be addressed.
Minerals 2023, 13(7), 926; https://doi.org/10.3390/min13070926
Submission received: 12 June 2023 / Revised: 7 July 2023 / Accepted: 8 July 2023 / Published: 10 July 2023
(This article belongs to the Special Issue Geochemical and Mineralogical Characteristics of Palaeokarstic Bauxite Deposits)
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Abstract

:
The Huri bauxite deposit is located 40 km northwest of Maragheh City, East Azerbaijan province, northwestern Iran. Bauxite horizons at Huri develop within karstic depressions and sinkholes of carbonate footwalls of the Ruteh Formation, overlain by carbonate of the Elika Formation. Powder X-ray diffraction (PXRD) and scanning electron microscope, coupled with energy dispersive X-ray spectroscopy (SEM-EDS) analyses show that the Huri bauxite ores consist of hematite, diaspore, kaolinite, and lesser amounts of halloysite, pyrophyllite, illite, goethite, clinochlore, amesite, rutile, zircon, and monazite. Based on geochemical studies (Eu/Eu* vs. Sm/Nd and U/Th bivariate diagrams), basalt rocks interbedded in limestone of the Ruteh Formation are the possible precursor rocks of the Huri bauxite deposit. The pH variations of weathering solutions, fluctuations in the groundwater table level, the function of carbonate bedrock as a geochemical barrier, simultaneous precipitation of Fe-bearing minerals, and preferential scavenging of light rare earth elements (LREE) by hematite played an important role in the fractionation of LREE from heavy rare earth elements (HREE) in the Huri bauxite ores. Fluctuations in groundwater table level, increasing pH of acidic solutions percolating downward, preferential adsorption of Ce onto hematite at the base of the profile, and the possible presence of Ce-bearing fluorocarbonates played an important role in increasing Ce anomaly from the top of the profile downward.

1. Introduction

Due to their expanding use in new technological applications and the global growing demand for these elements, critical elements, including rare earth elements (REE), have gained increasing attention in the past decade [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. The exploitation of ore deposits shows the importance of these elements; therefore, the great challenge facing us at the moment is exploring new economic sources for these elements. These strategic elements are generally concentrated in specific rock materials under certain geological environments. Bauxite deposits are among the specific rock materials that have the potential to significantly concentrate critical metals, making them precious for the exploration of these elements. Karst-type bauxite deposits, which are products of chemical weathering of aluminosilicate-rich parent rocks, accumulated on underlying karstified carbonates and in addition to the primary ore sources of aluminum, contain several economically important elements, including Co, V, Ti, Nb, Ga, Hf, Ta, Zr, Y, and REE [13,14,18,19,20]. These host of critical elements makes karst-type bauxite deposits, especially across the eastern Tethyan belt, worth considering further.
The Iranian karst-type bauxite deposits are deposited within karstic depressions and sinkholes of the Mesozoic marine carbonate deposits in the Palaeo-Tethys Ocean [21]. In recent years, several studies have been conducted on geological features, parental affinity, genetic characteristics and weathering mechanisms, and mineralogical and geochemical controls in the enrichment and distribution of elements, especially REE, of the Iranian bauxite deposits [12,13,14,20,22,23,24]. However, no comprehensive studies have been carried out on the Huri bauxite deposit, 40 km northwest of Maragheh City, East Azerbaijan province, northwestern Iran. The main goals of this study were to (1) determine the possible source rock of the deposit and (2) determine the factors controlling the distribution and fractionation of REE along a weathered profile of the Huri bauxite deposit, Maragheh City, East Azerbaijan province, northwestern Iran.

2. Geology of the Deposit

The Huri bauxite deposit is located 40 km northwest of Maragheh City, East Azerbaijan province, northwestern Iran (Figure 1a). According to the tectono-metamorphic zonation of Iran [25], the Huri bauxite deposit occurs within the Alborz–Azerbaijan zone. The oldest rock units in the study area are early Cambrian micaceous silty shales, dolomites, and sandstones of the Zaigun Formation. These rock units are overlain by early Cambrian arkosic sandstones of the Lalun Formation and middle Cambrian carbonate, sandstone, and shale of the Mila Formation. The Devonian limestone, diorite, and alternating dolomite and sandstone are overlain by early Permian sandstones of the Dorud Formation, middle Permian basalts, and limestones of the Ruteh Formation. The Triassic stratigraphic units consist of a thick sequence of sedimentary rocks. They include early–middle Triassic dolomite and dolomitic limestone of the Elika Formation and late Triassic sandstone and shale of the Nayband Formation. The youngest rock units are Neogene conglomerate, agglomerate, and breccia with a lesser amount of lahar and pyroxene andesite and Quaternary alluvial sediments (Figure 1b).
At Huri, sedimentary hiatus at the contact of limestone of the Ruteh Formation and dolomite and dolomitic limestone of the Elika Formation is associated with the generation and development of bauxite horizons. Bauxite horizons are developed within karstic depressions and sinkholes of carbonate footwall of the Ruteh Formation, overlain by carbonate of the Elika Formation. There is sharp contact between bauxite horizons and limestone of the Ruteh Formation and carbonate of the Elika Formation. Limestone from the Ruteh Formation with a gray color that acts as a bedrock for bauxite horizons contains calcite veinlets, along with cherty bands and nodules. The bauxite horizons have an overall NW–SE trend, a total length of 4 km, and a variable thickness of 4–15 m. Bauxite horizons are sometimes displaced by extensional faults.
According to field observations and physical features such as color, along one of the bauxite horizons, from base to top of the profile, the bauxite subsets are: (1) brownish red bauxite ores (BRBO), (2) brown bauxite ores (BBO), and (3) red bauxite ores (RBO). Among these bauxite subsets, the RBO is mostly layered and has the lowest hardness and density, whereas the BRBO and BBO are massive and dense and are harder and denser than the RBO. Limonitization is one of the most important characteristics of RBO and BBO, indicating the role of atmospheric waters and supergene oxidation. The increasing size of spheroids in bauxite samples, especially in iron nodules close to the carbonate bedrock of the Ruteh Formation, is observed.

3. Sampling and Analytical Methods

A total of 28 bauxite ores from a 14-meter-depth weathered profile were analyzed. Samples R-01–R-07 are from the RBO subset, samples R-08–R-15 are from the BBO subset, and samples R-16–R-28 are from the BRBO subset (Figure 2a). Additionally, 4 samples from Permian limestones footwall of the Ruteh Formation (L-01–L-04) and 4 samples from basalts interbedded in the Ruteh Formation (B-01–B-04) were analyzed. The semi-quantitative (wt%) mineralogical composition of 28 bauxite samples was determined using powder X-ray diffraction (PXRD) at the Geological Survey of Iran, Tehran. PXRD analysis was performed using a Siemens D5000 X’Pert powder diffractometer with Cu-Kα radiation at a voltage of 40 kV and a current of 30 mA with a step size of 0.02° in the 2θ range from 2° to 60°. Microchemical analysis was carried out at the Razi Metallurgical Research Center, Iran, using a Hitachi S-3400N scanning electron microscope equipped with a Link Analytical Oxford IE 350 energy dispersive X-ray spectrometer (SEM–EDS).
A 0.25 g of whole powdered samples from the bauxite ores, basalt, and limestone were fused with a flux of lithium tetraborate–lithium metaborate, heated in a furnace at 1000 °C, and then dissolved in 100 mL 5% HNO3. Major oxides and U, Th, Y, and REE concentrations were determined using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), respectively, at Activation Laboratories Ltd. (Actlabs) in Vancouver, Canada. Loss on ignition (LOI) was estimated based on weight difference after heating at 950 °C.

4. Results

4.1. Mineralogical and Textural Features

Based on petrographic observations, the Huri bauxite ores have a pelitomorphic and microgranular matrix with spheroidal to ovoid components such as ooids and pisoids embedded in the pelitomorphic matrix. The studied bauxite samples display ooidic (100–1000 μm), pisoidic (1–5 mm), spastoidic, and nodular textures, following the terms proposed by Bárdossy [26]. Hematite was the only mineral phase identified in the studied bauxite samples by microscopic observations and occurs in the form of layering, secondary coatings around spheroidal components, and also in the core of ooids and pisoids (Figure 3a–d). Some researchers [27,28] believed that ferruginous nodules generated during chemical weathering of parent rock under tropical and subtropical climatic conditions are indicative of fluctuations in groundwater levels during the evolution of the deposit. These textural components are prevalent in the Mediterranean-type karst bauxites [27,28]. Fe-rich coatings around spheroidal components (Figure 3b) can be attributed to the distribution and migration of Fe and its precipitation under suitable Eh–pH conditions. The elongated and/or sinusoidal forms in ooids and pisoids can be associated with deformations in a semi-plastic state [29] or to re-depositional conditions during the evolution of the deposit [28].
The semi-quantitative mineralogical composition of 28 bauxite samples from the Huri deposit is given in Table 1. There was no significant variation in the mineralogical composition of the bauxite samples along the studied profile, as shown in Figure 2b and Figure 4. PXRD analyses showed that the Huri bauxite ores consist of hematite, diaspore, and kaolinite—accounting for 76–96% of the total mineral assemblage in the samples—and lesser amounts of halloysite, pyrophyllite, illite, goethite, clinochlore, amesite, and rutile (Figure 4). There is a gradual increase in the abundance of hematite from the top to the base of the profile, in striking contrast to a downward decrease in abundance of diaspore and, to a lesser extent, clay minerals such as kaolinite, illite, clinochlore, and halloysite. Hematite was the most abundant in the BRBO subset ores, significantly close to carbonate bedrocks of the Ruteh Formation. Halloysite and clinochlore occur in the RBO subset ores only, and goethite is present in the two upper RBO and BBO subsets of the profile. Based on the SEM-EDS observations, minerals resistant to weathering zircon and monazite-(Ce) are present as rounded or elliptical single grains in the RBO and BBO subsets, respectively, embedded in a kaolinite matrix (Figure 5a,b).

4.2. Geochemistry

4.2.1. Major Oxides

The dominant chemical components in the analyzed bauxite samples are Al2O3, SiO2, and Fe2O3, accounting for 80.41–88.23 wt% of the total content of the samples (Table 2). SiO2 contents in the RBO (24.19–26.41 wt%) and BBO (20.39–25.67 wt%) subsets are higher than in the BRBO subset (15.79–20.36 wt%), corresponding to a higher abundance of clay minerals such as kaolinite, illite, clinochlore, and halloysite. In contrast, Fe2O3 contents in the BRBO (32.17–47.85 wt%) and BBO (15.36–33.21 wt%) subsets are higher than in the RBO subset (11.53–16.14 wt%), corresponding to a higher abundance of hematite. Geochemical results are consistent with mineralogical evolution upward the succession, promoting an increase in the abundance of diaspore and clay minerals such as kaolinite, illite, clinochlore, and halloysite, and a decrease in the abundance of hematite, a feature observed in other Mediterranean-type karst bauxite deposits. The TiO2 content in the analyzed bauxite samples is up to a maximum of 4.38 wt%. Major oxides Na2O, K2O, CaO, MgO, MnO, and P2O5 were detected at significantly lower concentrations, accounting for 0.90–2.68 wt% of the total content of the samples. Major oxides Al2O3, SiO2, and Fe2O3 are the dominant constituents of the analyzed basalt samples, accounting for 74.62–77.31 wt% of the total content of the samples, whereas other oxides show a wide range (0.39–7.41 wt%) in content. CaO is the dominant constituent of the analyzed limestone samples of the Ruteh Formation, and other oxides are present at low concentrations, up to a maximum of 8.9 wt%.

4.2.2. Trace Elements

The light rare earth elements (LREE: La–Sm), heavy rare earth elements (HREE: Eu–Lu), and total rare earth elements (ΣREE: La–Lu) content in the Huri bauxite ores are in the range 197.2–368.5 ppm LREE, 20.9–46.7 ppm HREE, and 218.1–413.2 ppm REE (Table 2). They are 80.4–102.4 ppm LREE, 17.4–19.2 ppm HREE, and 98.0–121.6 ppm REE in the basalt rocks, and 7.9–13.3 ppm LREE, 1.2–2.2 ppm HREE, and 9.1–15.5 ppm REE in the carbonate bedrock of the Ruteh Formation. The Y content in the Huri bauxite ores is in the range of 7.8–101.3 ppm. The concentration of this element in the basalt rocks and the carbonate rocks of the Ruteh Formation ranges from 9.3–12.7 ppm and 1.2–3.2 ppm, respectively (Table 2).
There is an increase in the LREE, HREE, and REE contents from the lower and middle parts of the profile (the BRBO and BBO subset ores) upward toward the RBO subset ores. The (LREE/HREE)N and La/Y ratios representing the fractionation of LREE from HREE in the Huri bauxite ores are in the range 4.7–6.3 and 0.7–6.4, respectively. These ratios are in the range 2.9–3.4 (LREE/HREE)N and 1.4–2.2 La/Y for the basalt rocks, and 3.8–4.2 (LREE/HREE)N and 0.8–1.8 La/Y for the carbonate bedrock of the Ruteh Formation. The BRBO subset ores are characterized by higher (LREE/HREE)N and La/Y ratios than the two upper BBO and RBO subset ores. It indicates a higher accumulation of REE in the uppermost parts of the succession, but a higher LREE/HREE fraction downward toward the BRBO subset ores. The BRBO subset ores (Ce/Ce* = 1.1–2.0) have a slightly higher Ce anomaly than the BBO (Ce/Ce* = 0.9–1.4) and RBO (Ce/Ce* = 0.8–1.0) subset ores. Negative Eu anomalies (0.76–0.94) are observed in the studied samples from three subsets, but higher anomalies are present in the ores at the basal part of the profile. The Eu and Ce anomalies are in the range 0.85–0.90 Eu/Eu* and 0.82–0.86 Ce/Ce* for the basalt rocks, and 0.30–0.39 Eu/Eu* and 0.66–0.84 Ce/Ce* for the carbonate bedrock of the Ruteh Formation.
The U and Th contents in the Huri bauxite ores are in the range of 11.5–22.6 ppm and 20.8-29.3 ppm, respectively. The concentrations of U and Th in the basalt rocks are in the range 14.2–15.9 and 17.9–18.8 ppm, respectively, whereas U and Th contents in the carbonate rocks of the Ruteh Formation are 0.3–1.3 ppm and 0.08–0.41 ppm, respectively (Table 2).

5. Discussion

5.1. Mineralogy

Breakdown of primary constituents of parent rock results in the generation of pedogenetic phyllosilicates, such as kaolinite, and Fe (oxyhydr)oxides during weathering processes. The decomposition of labile aluminosilicate minerals of the parent rocks, such as muscovite and feldspar, causes the generation of kaolinite under warm and humid tropical climates. According to Schellmann [32], the formation of Fe-rich minerals such as hematite and goethite is associated with the dissolution of ferromagnesian minerals and also with redox conditions controlled by water activity. Hematite is the main Fe-bearing mineral in the Huri bauxite deposit. This mineral forms at a pH range of 7–8 and reflects an oxidizing environment during bauxitization. According to Bárdossy and Aleva [33], the increasing downward trend of hematite reflects multiple cycles of groundwater mobilization and re-distribution. A significant downward increase in hematite is consistent with the classification of the ores in the SiO2–Al2O3–Fe2O3 ternary modified from Aleva [34] in which the RBO subset ores fall within the field of bauxite, whereas the BBO and BRBO subset ores mainly occur in the laterite field (Figure 6). A downward increase in lateritization degree and abundance of Fe contents and Fe minerals shown in Figure 6 are probably an interplay between groundwater and the vertical downward increase in penetrating weathering front, as already noted by Bárdossy and Aleva [33]. These findings are consistent with the point that lithological and geochemical characteristics of the bauxite samples control weathering intensity, weathering trend, and bauxitization processes. The occurrence of both goethite and hematite in the bauxite ores in the uppermost parts of the profile is thought to be a result of weathering in an oxygenated condition without complete dehydration of goethite [33]. The content of resistant accessory minerals mainly depends on the chemical composition of precursor rock and the degree of chemical weathering because these resistant minerals are derived from weathering parent material [6]. According to Cetiner et al. [35], the presence of minerals resistant to weathering, such as monazite in the BBO subset and zircon in the RBO subset, is consistent with the fact that the solubility of these minerals is very low at ambient temperature and low pH.

5.2. Parental Affinity of the Deposit

Addressing the provenance of karst bauxite deposits, especially of allochthonous karst bauxite deposits, is debatable due to significant fractionation of major and trace elements during chemical weathering [22,36]. Although carbonate rocks can host karst bauxites, they cannot generally be considered a suitable parent material for karst bauxite deposits. Based on various studies carried out on the Iranian karst bauxite deposits by many researchers in recent years, igneous rocks—mainly of mafic composition—and argillaceous limestone have been suggested as the parent rock of these deposits [21]. Since Eu anomalies in the bauxite samples from the Huri deposit show negligible variation, ranging from 0.76 to 0.94, thus this ratio can be considered a conservative index, as Eu anomaly was considered to be retained during intense weathering [12,22,36]. Likewise, the Sm/Nd ratio has been applied to identify parent rocks of bauxite deposits due to minor fractionation of elements Sm and Nd during weathering processes, as stated by several researchers [12,13,22,23]. Geochemical proxies such as Nb/Ta, Al/Ta, Ti/Zr, Al2O3/Hf, Al2O3/Nb, and TiO2/Al2O3 have been successfully used to recognize the provenance of bauxite deposits [12,20,23,36,37,38,39]. In spite of the fact that there is no completely immobile element in weathering environments, a strong positive correlation between Th and U (r = 0.85) shows that these elements are probably less mobile during the formation of the Huri bauxite deposit and are used as reference elements in this study. On the Eu/Eu* vs. Sm/Nd and U/Th bivariate diagrams, the Huri bauxite samples are far from the carbonate bedrock of the Ruteh Formation, but close to the basalt samples (Figure 7). This suggests that basalt rocks are the possible precursor rocks of the Huri bauxite deposit, consistent with the sporadic occurrence of basalt patches in the Ruteh Formation in different parts of northwestern Iran.

5.3. Factors Controlling Distribution and Fractionation of REE

Fractionation of major and trace elements (including REE) occurs during weathering processes and bauxitization. Degree of bauxitization and REE content in bauxite samples depend on a number of factors, including chemical and mineralogical composition of parent material, thickness of deposit, duration of weathering processes, drainage, climate, topography, groundwater table position, and microbial activity [33,40]. REE released from primary minerals of parent rock during weathering processes occur in mineral lattice of REE-bearing minerals, as substitutes for major constituents in minerals like apatite and fluorite, and/or are absorbed onto certain mineral surfaces that could be a residual primary mineral or a newly formed mineral. In fact, the presence of REE authigenic minerals greatly influences REE distribution patterns of the ores. Furthermore, organic matter in the upper parts of the weathered profile have a high capacity to adsorb and chelate REE. The presence of organic matter and weathering-resistant REE-bearing minerals, such as monazite, in the uppermost parts of the succession and adsorption of REE onto clay minerals, such as kaolinite, halloysite, and clinochlore, are the other effective mechanisms for concentration and accumulation of REE in the upper parts of the Huri bauxite profile.
In addition to the nature of precursor rocks, physicochemical conditions of weathering environment, and complexation and adsorption mechanisms, the mobility and fractionation of REE during weathering processes can be associated with the preferential dissolution of certain REE minerals. Fractionation of LREE from HREE in bauxite samples can be explained by the formation of Fe (oxyhydr)oxides, clay minerals, and P-bearing minerals as scavengers of LREE. The presence of weathering-resistant REE-bearing minerals, such as monazite, leads to enrichment of LREE in the upper parts of the succession. Some geochemical investigations of bauxite deposits show that both LREE and HREE act as mobile elements during pedogenesis processes [41], while LREE in this study are more mobile than HREE during weathering, as stated by some researchers in the course of weathering [42]. This conclusion is manifested by a slightly increasing (LREE/HREE)N ratio from the top of the profile downward toward the BBO and BRBO subset ores (Figure 8a). In fact, the carbonate bedrock of the Ruteh Formation as a chemical barrier had a significant effect on increasing pH of acidic solutions percolating downward. Therefore, it suggests that pH was one of the key factors controlling the fractionation and mobility of REE in the weathered profile of the Huri bauxite deposit. As the pH of percolating acidic solutions increases downward the profile, the extent of REE-bearing minerals identified by SEM–EDS remarkably decreases. Mineral control (adsorption of LREE by hematite) may be an effective mechanism for the fractionation of LREE from HREE in the Huri bauxite samples, in which Fe content is much higher than Na, K, and P content. The La/Y ratio shows an uneven increase in the downward trend (Figure 8a). This ratio was used to determine the change in pH weathered environment during bauxitization. According to Crnički and Jurković [43], the La/Y ratio below and above 1 represents acidic and alkaline environments, respectively. The increasing downward La/Y ratio suggests alkaline conditions prevailing at the base of the Huri weathered profile. Erratic trends in (LREE/HREE)N and La/Y ratios in the Huri bauxite samples that represent leaching and concentration of REE along the studied profile are generally ascribed to fluctuations in the groundwater table level during the development and formation of the bauxite body. Groundwater fluctuations are generally controlled by seasonal successive changes in precipitation during rainy and dry seasons [33].
Cerium behaves differently from the other REE during chemical weathering processes. The distribution of Ce anomaly provides insights into paleo-redox evolution during the formation of bauxite deposits, as stated by several researchers [12,14,22]. According to previous research, positive Ce anomaly in bauxite deposits is generally attributed to the formation of cerianite via the oxidation of Ce(III) to Ce(IV) at pH = 5–6 [44]. In this case, a positive Ce anomaly is obvious at the bottom of the Huri bauxite profile. The BRBO subset ores exhibited a significant abundance of hematite, along with a pronounced positive Ce anomaly (Ce/Ce* = 1.1–2.0) especially close to the carbonate bedrock of the Ruteh Formation (Figure 8b). The reason for the positive Ce anomaly at the bottom of the weathering profile is adsorption of Ce onto hematite. There was a positive correlation between the Ce anomaly values of the analyzed samples and Fe content and Fe oxide abundance. Less abundant clay minerals, such as kaolinite, and more abundant Fe oxides in the samples showing positive Ce anomalies suggest that the variation in the Ce anomaly in the Huri bauxite deposit is associated with Fe behavior and not clay. Another reason for positive Ce anomaly toward the carbonate bedrock of the Ruteh Formation can be attributed to the formation of Ce-bearing fluorocarbonate mineral, parisite, (Ce2Ca(CO3)3F2). In general, REE mobilized under acidic conditions by Ce-depleted solutions percolating downward as fluoride/carbonate/carbonate–fluoride complexes are further concentrated as REE phosphate and fluorocarbonate minerals toward the carbonate bedrock barrier at alkaline pH. The conversion of Ce4+ to Ce3+, possibly associated with the rise in groundwater level, leads to the precipitation of parisite downward the succession [44]. However, this mineral was not identified by SEM–EDS in the Huri bauxite samples. As a whole, fluctuations in the groundwater table level and the carbonate bedrock of the Ruteh Formation as a geochemical barrier had significant effects on increasing pH of acidic solutions percolating downward and consequently Fe leaching and simultaneous precipitation of Fe-bearing minerals, such as hematite, and the preferential adsorption of Ce onto hematite in the lower parts of the profile. The negative Eu anomaly of the Huri bauxite samples (0.76–0.94) (Figure 8b) represents the decomposition of major constituents of parent rock, such as plagioclase, during weathering processes, and is a function of weathering intensity during the formation of the Huri bauxite deposit.

6. Conclusions

The Huri bauxite horizons occur within karstic depressions and sinkholes of carbonate bedrock of the Ruteh Formation, overlaid by the carbonate rocks of the Elika Formation. PXRD data revealed that the main mineral constituents of the Huri bauxite samples are hematite, diaspore, and kaolinite, accounting for 76–96% of the total mineral assemblage of the samples. Halloysite, pyrophyllite, illite, goethite, clinochlore, amesite, and rutile are accessory minerals identified in the analyzed Huri samples. A slightly increasing (LREE/HREE)N ratio from the top of the profile downward can be attributed to fluctuations in groundwater table level and the buffer effect of carbonate bedrock of the Ruteh Formation in increasing pH of acidic solutions percolating downward and the adsorption of LREE by hematite. The variation in the Ce anomaly in the Huri bauxite deposit may be associated with the Fe behavior, the adsorption of Ce onto hematite at the base of the profile, especially close to the carbonate bedrock of the Ruteh Formation, and fluctuations in groundwater table level, as well as the possible presence of Ce-bearing fluorocarbonates, downward the succession. Based on geochemical studies (Eu/Eu* vs. Sm/Nd and U/Th bivariate diagrams), basalt rocks interbedded in limestone of the Ruteh Formation are the possible precursor rocks of the Huri bauxite deposit.

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, 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 research received no external funding.

Data Availability Statement

Not applicable.

Acknowledgments

The project was supported by the Bureau of Research Affairs of Urmia University, to which we are grateful.

Conflicts of Interest

The authors declare no conflict of interest.

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Minerals 13 00926 g001 550
Figure 1. (a) Simplified tectonic map of Iran [25] showing the location of the Huri bauxite deposit in East Azerbaijan province, northwestern Iran. (b) A simplified geological map showing the local geological setting and lithological units of the Huri bauxite deposit.
Figure 1. (a) Simplified tectonic map of Iran [25] showing the location of the Huri bauxite deposit in East Azerbaijan province, northwestern Iran. (b) A simplified geological map showing the local geological setting and lithological units of the Huri bauxite deposit.
Minerals 13 00926 g001
Minerals 13 00926 g002 550
Figure 2. (a) Stratigraphic column of the bauxite samples along the selected profile at Huri (refer to Figure 1b for the position and trend of the selected profile). The position of samples selected for geochemical analyses is marked with filled circles. (b) Variations in the mineralogical composition of the bauxite samples along the selected profile at Huri.
Figure 2. (a) Stratigraphic column of the bauxite samples along the selected profile at Huri (refer to Figure 1b for the position and trend of the selected profile). The position of samples selected for geochemical analyses is marked with filled circles. (b) Variations in the mineralogical composition of the bauxite samples along the selected profile at Huri.
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Minerals 13 00926 g003 550
Figure 3. Photomicrographs showing petrological aspects in the Huri bauxite deposit. (a–d) The occurrence of hematite in the form of layering, secondary coatings around spheroidal components, and the core of ooids and pisoids. All images were taken under reflected light. Abbreviations: Hem = hematite [30].
Figure 3. Photomicrographs showing petrological aspects in the Huri bauxite deposit. (a–d) The occurrence of hematite in the form of layering, secondary coatings around spheroidal components, and the core of ooids and pisoids. All images were taken under reflected light. Abbreviations: Hem = hematite [30].
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Figure 4. Powder-XRD patterns of representative bauxite samples from the Huri deposit. Ame = amesite, Dsp = diaspore, Gth = goethite, Hal = halloysite, Hem = hematite, Ilt = illite, Kln = kaolinite, Prl = pyrophyllite, Rt = rutile; mineral abbreviations from [30].
Figure 4. Powder-XRD patterns of representative bauxite samples from the Huri deposit. Ame = amesite, Dsp = diaspore, Gth = goethite, Hal = halloysite, Hem = hematite, Ilt = illite, Kln = kaolinite, Prl = pyrophyllite, Rt = rutile; mineral abbreviations from [30].
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Figure 5. SEM–EDS results of the Huri bauxite deposit, East Azerbaijan province, northwestern Iran. (a) Zircon and kaolinite in sample R-02 from the RBO subset. (b) Monazite and diaspore in sample R-09 from the BBO subset. Abbreviations: Dsp = diaspore, Kln = kaolinite, Zrn = zircon, Mnz = monazite [30].
Figure 5. SEM–EDS results of the Huri bauxite deposit, East Azerbaijan province, northwestern Iran. (a) Zircon and kaolinite in sample R-02 from the RBO subset. (b) Monazite and diaspore in sample R-09 from the BBO subset. Abbreviations: Dsp = diaspore, Kln = kaolinite, Zrn = zircon, Mnz = monazite [30].
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Figure 6. Al2O3–SiO2–Fe2O3 ternary plots [32,34] showing mineralogical classification and lateritization degree of the Huri bauxite samples.
Figure 6. Al2O3–SiO2–Fe2O3 ternary plots [32,34] showing mineralogical classification and lateritization degree of the Huri bauxite samples.
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Figure 7. Bivariate plots of Eu/Eu* vs. Sm/Nd (a) and U/Th (b) representing affinity of the Huri bauxite samples with basalt rocks interbedded in limestone of the Ruteh Formation.
Figure 7. Bivariate plots of Eu/Eu* vs. Sm/Nd (a) and U/Th (b) representing affinity of the Huri bauxite samples with basalt rocks interbedded in limestone of the Ruteh Formation.
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Figure 8. Variation trend of (a) (LREE/HREE)N and La/Y, and (b) Ce/Ce* and Eu/Eu* for the Huri bauxite deposit.
Figure 8. Variation trend of (a) (LREE/HREE)N and La/Y, and (b) Ce/Ce* and Eu/Eu* for the Huri bauxite deposit.
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Table
Table 1. Results of semi-quantitative mineralogical analysis (weight percent, wt%) of 28 samples from the Huri bauxite deposit, East Azerbaijan province, northwestern Iran. Ame = amesite, Clc = clinochlore, Dsp = diaspore, Gth = goethite, Hal = halloysite, Hem = hematite, Ilt = illite, Kln = kaolinite, Prl = pyrophyllite, Rt = rutile; mineral abbreviations from [30].
Table 1. Results of semi-quantitative mineralogical analysis (weight percent, wt%) of 28 samples from the Huri bauxite deposit, East Azerbaijan province, northwestern Iran. Ame = amesite, Clc = clinochlore, Dsp = diaspore, Gth = goethite, Hal = halloysite, Hem = hematite, Ilt = illite, Kln = kaolinite, Prl = pyrophyllite, Rt = rutile; mineral abbreviations from [30].
Sample No.Bauxite SubsetDspHemKlnHalIltGthClcAmePrlRt
R-01Red bauxite ore (RBO)4862225732–5
R-02Red bauxite ore (RBO)49723–563124
R-03Red bauxite ore (RBO)488232362224
R-04Red bauxite ore (RBO)51921245–134
R-05Red bauxite ore (RBO)469251452224
R-06Red bauxite ore (RBO)4611242342134
R-07Red bauxite ore (RBO)471325–3422–4
R-08Brown bauxite ore (BBO)461424–44–224
R-09Brown bauxite ore (BBO)442022–43–214
R-10Brown bauxite ore (BBO)432221–33–224
R-11Brown bauxite ore (BBO)432519–32–224
R-12Brown bauxite ore (BBO)442222–42–2–4
R-13Brown bauxite ore (BBO)412522–32–124
R-14Brown bauxite ore (BBO)392822–32––24
R-15Brown bauxite ore (BBO)373121–31–124
R-16Brownish red bauxite ore (BRBO)353321–3––224
R-17Brownish red bauxite ore (BRBO)363520–3––114
R-18Brownish red bauxite ore (BRBO)373619–3––1–4
R-19Brownish red bauxite ore (BRBO)373519–3–––24
R-20Brownish red bauxite ore (BRBO)393717–2––1–4
R-21Brownish red bauxite ore (BRBO)373818–2–––23
R-22Brownish red bauxite ore (BRBO)393818–2––––3
R-23Brownish red bauxite ore (BRBO)363917–2––213
R-24Brownish red bauxite ore (BRBO)294717–2–––23
R-25Brownish red bauxite ore (BRBO)284817–1––123
R-26Brownish red bauxite ore (BRBO)314916–1––––3
R-27Brownish red bauxite ore (BRBO)295015–1––113
R-28Brownish red bauxite ore (BRBO)295015–1––113
Table
Table 2. Major-element oxides (in weight percent) and trace-element concentrations (in ppm) of the bauxite samples, basalt rocks interbedded in the limestone of the Ruteh Formation, and carbonate of the Ruteh Formation from the Huri bauxite deposit, East Azerbaijan province, northwestern Iran.
Table 2. Major-element oxides (in weight percent) and trace-element concentrations (in ppm) of the bauxite samples, basalt rocks interbedded in the limestone of the Ruteh Formation, and carbonate of the Ruteh Formation from the Huri bauxite deposit, East Azerbaijan province, northwestern Iran.
BasaltRBO
d.l.B-01B-02B-03B-04R-01R-02R-03R-04R-05R-06R-07
SiO20.0151.8851.0450.3250.6325.5624.8824.1925.5525.1525.6926.41
TiO20.012.042.122.162.254.384.264.134.053.993.874.03
Al2O30.0111.9612.5113.9813.9345.5544.5443.5242.0540.5839.4141.32
Fe2O3(T)0.0112.9813.7610.8710.0611.5313.6515.7415.3315.0216.1415.21
MnO0.010.880.910.930.960.210.190.190.180.170.150.16
MgO0.014.445.565.964.750.790.760.740.710.720.750.81
CaO0.016.174.727.117.410.030.020.030.040.060.050.03
Na2O0.014.112.924.334.510.010.010.010.010.010.020.02
K2O0.013.883.892.283.231.551.661.221.621.521.331.25
P2O50.010.390.410.670.710.050.040.050.060.070.090.15
LOI 0.011.252.091.021.0110.339.9810.1210.3912.5112.2510.52
Sum0.0199.9899.9399.6399.4599.9999.9999.9599.9999.8099.7599.91
U 0.0515.1114.2115.9214.8722.6921.1420.5521.2420.9318.5020.58
Th0.0518.7017.9018.8018.2029.2529.3428.4725.9126.3426.2327.13
Y0.59.311.112.710.497.395.592.391.3100.790.7100.5
La 0.517.222.717.422.586.180.574.985.495.976.190.7
Ce0.531.641.332.741.1139.4144.5149.6150.7151.8155.3151.2
Pr0.034.846.524.796.5321.3819.6817.9820.3422.7118.5221.53
Nd0.121.626.321.526.579.172.565.974.382.768.478.5
Sm0.035.125.625.085.6114.8613.7412.6213.9815.3413.1314.66
Eu0.031.571.611.521.644.103.783.473.834.193.604.01
Gd0.055.555.885.515.8613.0012.1911.3812.0712.7611.8112.41
Tb0.010.770.880.760.872.071.931.791.892.001.861.95
Dy0.054.714.904.734.8811.8511.0810.3110.8111.3110.8411.06
Ho0.010.780.910.750.892.242.111.972.032.092.092.06
Er0.032.032.431.972.416.255.885.515.665.815.865.74
Tm0.010.260.310.240.320.880.830.780.800.810.830.80
Yb0.031.762.021.732.015.455.134.804.925.045.094.98
Lu0.010.240.260.210.240.830.780.740.750.770.780.76
LREE (La–Sm) –80.36102.4481.47102.24340.84330.92321.00344.72368.45331.45356.59
HREE (Eu–Lu) –17.6719.2017.4219.1246.6743.7140.7542.7644.7842.7643.77
REE (La–Lu) –98.03121.6498.89121.36387.51374.63361.75387.48413.23374.21400.36
(LREE/HREE)N–2.903.402.983.414.664.835.035.145.254.955.20
La/Y–1.852.051.372.160.880.840.810.940.950.840.90
Eu/Eu*–0.900.850.870.870.880.870.870.880.890.870.89
Ce/Ce*–0.840.820.860.820.770.860.970.860.770.980.81
BBOBRBO
R-08R-09R-10R-11R-12R-13R-14R-15R-16R-17R-18R-19
SiO225.6722.8524.4820.9423.1121.3320.5820.3919.8119.7818.9120.36
TiO24.023.873.813.713.843.713.643.523.553.583.423.51
Al2O342.0741.5238.3136.0938.5237.1534.9931.6232.8532.8430.3631.61
Fe2O3(T)15.3619.9921.2227.6622.2426.0929.1533.2132.1832.1734.1533.19
MnO0.150.140.150.150.120.110.090.070.070.060.070.08
MgO0.790.710.710.650.680.620.610.590.520.570.560.59
CaO0.030.040.050.050.080.060.070.090.080.070.090.11
Na2O0.010.010.020.030.020.030.030.040.040.040.050.04
K2O1.541.220.850.871.060.880.550.430.610.490.460.41
P2O50.140.160.140.140.150.150.140.130.130.130.130.13
LOI 10.219.4810.259.6910.179.8610.149.8810.1110.2511.749.81
Sum100.00100.00100.0099.9899.9999.9999.99100.0099.9599.9899.9099.84
U 19.8719.4418.2517.8918.5117.9917.7816.6816.5116.8815.7916.68
Th29.0025.7026.0026.1226.0526.0426.1925.8026.3526.3525.2025.75
Y101.388.977.816.126.124.121.716.919.719.814.116.9
La 85.463.865.251.867.454.249.447.944.644.651.347.9
Ce150.7159.9151.1143.5145.5146.8140.3129.4133.7133.7125.1129.4
Pr20.3414.6015.5012.0315.9312.5411.5210.7010.5010.5010.8010.65
Nd74.352.857.043.958.245.742.138.938.638.639.338.9
Sm13.9810.4010.908.3210.958.747.917.207.097.097.407.24
Eu3.832.803.002.353.042.452.252.102.062.062.102.09
Gd12.079.8010.107.949.828.317.586.706.856.856.606.71
Tb1.891.501.601.281.561.331.241.101.151.151.101.11
Dy10.818.809.407.759.187.957.556.807.147.146.506.79
Ho2.031.701.801.541.771.571.501.401.441.441.301.35
Er5.664.805.204.495.044.544.434.104.324.323.804.05
Tm0.800.700.700.630.710.640.620.600.610.610.500.57
Yb4.924.204.503.914.393.963.863.603.763.763.403.55
Lu0.750.600.700.600.670.610.590.500.570.570.500.54
LREE (La–Sm) 344.72301.50299.70259.55297.98267.98251.23234.10234.49234.49233.90234.09
HREE (Eu–Lu) 42.7634.9037.0030.4936.1831.3629.6226.9027.9027.9025.8026.76
REE (La–Lu) 387.48336.40336.70290.04334.16299.34280.85261.00262.39262.39259.70260.85
(LREE/HREE)N5.145.515.175.435.255.455.415.555.365.365.785.58
La/Y0.840.720.843.222.582.252.282.832.262.253.642.83
Eu/Eu*0.880.830.860.870.880.870.880.910.890.890.900.90
Ce/Ce*0.861.241.131.361.051.331.391.341.461.461.241.35
BRBOLimestone
R-20R-21R-22R-23R-24R-25R-26R-27R-28L-01L-02L-03L-04
SiO218.7418.0617.6316.2516.7416.1616.1215.7915.960.511.325.614.32
TiO23.333.223.093.272.872.812.842.822.850.020.010.030.02
Al2O329.1527.9226.8528.5224.6224.2224.4224.3324.410.240.361.090.45
Fe2O3 (T)35.1636.1537.9435.6446.1247.8547.0147.7547.320.210.360.750.41
MnO0.060.060.070.060.050.030.040.030.040.060.040.030.05
MgO0.540.540.520.470.480.460.390.360.430.651.931.240.72
CaO0.120.130.150.140.150.160.160.140.1554.8452.3150.4152.36
Na2O0.050.050.060.050.060.060.060.060.060.060.050.020.03
K2O0.460.480.220.290.170.190.160.190.120.030.050.090.13
P2O50.120.110.130.120.130.120.120.120.130.030.020.030.03
LOI 12.1212.9912.9914.997.957.928.678.398.4543.2142.7140.1241.06
Sum99.8599.7099.7099.8099.00100.00100.0099.9899.9099.8699.1699.4299.58
U 14.8914.0012.7214.4511.8411.5611.7411.6511.710.620.331.071.32
Th24.5524.0023.6024.2521.0021.0021.0020.8120.900.080.110.410.25
Y9.69.67.88.89.811.612.111.112.41.21.63.22.2
La 54.657.933.456.230.129.629.929.729.81.72.82.72.3
Ce120.8116.5129.2118.6125.8125.4125.6125.5125.62.14.63.83.9
Pr10.9611.107.5011.047.347.347.307.347.300.310.630.550.52
Nd39.639.928.539.728.428.528.428.428.43.54.74.54.4
Sm7.547.706.107.616.346.386.406.376.400.270.610.550.52
Eu2.172.201.802.191.581.531.601.541.600.030.060.070.06
Gd6.426.305.606.355.705.665.705.675.700.310.620.530.55
Tb1.031.000.901.010.950.951.000.951.000.070.130.120.11
Dy6.105.805.405.935.535.515.505.515.500.310.620.560.53
Ho1.191.101.101.151.061.051.101.051.100.070.130.130.11
Er3.503.203.103.362.972.922.902.932.900.180.230.250.22
Tm0.500.500.500.480.420.410.400.410.400.030.040.030.04
Yb3.142.902.803.032.552.482.502.492.500.170.320.310.26
Lu0.480.500.400.470.380.360.400.360.400.030.040.050.04
LREE (La–Sm) 233.50233.10204.70233.15197.98197.22197.60197.31197.507.8813.3412.1011.64
HREE (Eu–Lu) 24.5323.5021.6023.9721.1420.8721.1020.9121.101.202.192.051.92
REE (La–Lu) 258.03256.60226.30257.12219.12218.09218.70218.22218.609.0815.5314.1513.56
(LREE/HREE)N6.076.336.056.215.986.035.986.025.974.193.893.773.87
La/Y5.696.034.286.393.072.552.472.682.401.421.750.841.05
Eu/Eu*0.930.940.920.940.790.760.790.770.790.320.300.390.34
Ce/Ce*1.141.051.921.102.012.032.022.022.030.660.810.720.84
Abbreviations: dl = detection limit, LOI = loss on ignition. Eu/Eu* = (2 × EuN)/(SmN + GdN), Ce/Ce* = (2 × CeN)/(LaN + PrN), (LREE/HREE)N = (LREE/HREE)bauxite ore/(LREE/HREE)chondrite, where the subscript “N” refers to normalized values to chondrite [31].
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Abedini, A.; Khosravi, M. REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, Northwestern Iran. Minerals 2023, 13, 926. https://doi.org/10.3390/min13070926

AMA Style

Abedini A, Khosravi M. REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, Northwestern Iran. Minerals. 2023; 13(7):926. https://doi.org/10.3390/min13070926

Chicago/Turabian Style

Abedini, Ali, and Maryam Khosravi. 2023. "REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, Northwestern Iran" Minerals 13, no. 7: 926. https://doi.org/10.3390/min13070926

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