Geochemical constraints on the Triassic–Jurassic Amir-Abad karst-type bauxite deposit, NW Iran

Journal Pre-proof Geochemical constraints on the Triassic–Jurassic Amir-Abad karst-type bauxite deposit, NW Iran

Ali Abedini, Maryam Khosravi PII:

S0375-6742(19)30259-6

DOI:

https://doi.org/10.1016/j.gexplo.2020.106489

Reference:

GEXPLO 106489

To appear in:

Journal of Geochemical Exploration

Received date:

7 May 2019

Revised date:

17 October 2019

Accepted date:

28 January 2020

Please cite this article as: A. Abedini and M. Khosravi, Geochemical constraints on the Triassic–Jurassic Amir-Abad karst-type bauxite deposit, NW Iran, Journal of Geochemical Exploration (2018), https://doi.org/10.1016/j.gexplo.2020.106489

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© 2018 Published by Elsevier.

Journal Pre-proof

Geochemical constraints on the Triassic–Jurassic Amir-Abad karst-type bauxite deposit, NW Iran

Ali Abedinia, *, Maryam Khosravib

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,* Department of Geology, Faculty of Sciences, Urmia University, 57153165, Urmia, Iran (Tel: +98-44-

Department of Earth Sciences, College of Sciences, Shiraz University, Shiraz 71454, Iran

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b

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32972134; Fax: +98-44-32753172)

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* Corresponding author.

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Email address: [email protected] and [email protected].

Abstract

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The Amir-Abad karst-type bauxite deposit is located in the Irano–Himalayan bauxite belt, 8 km of south of Maragheh city in northwestern Iran. The bauxite ores occur as layers and lens-shaped pockets in the contact of

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the Triassic dolomitic limestone of the Elika Formation and the Lower Jurassic sandstone, siltstone, shale, and

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coal of the Shemshak Formation. Based on the PXRD and SEM-EDS analyses, the bauxite ores mainly consist of diaspore, hematite, and kaolinite group minerals (e.g., kaolinite and montmorillonite), with lesser amounts of goethite, anatase/rutile, and zircon. Nickel, Cr, Co, and V show a pattern similar to Fe; they were leached from the uppermost parts of the profile by acidic percolating solutions, and concentrated toward the carbonate bedrock under alkaline conditions. Aluminum, Nb, Ga, Ta, Th, Hf, and Zr can be regarded as less mobile elements. Variations of the La/Y, (ΣLREE/ΣHREE)N, and (La/Yb)N ratios across the weathering profile, together with leaching of alkali and alkaline earth metals indicate an acidic environment in the uppermost parts, and a basic environment in the basal parts of the profile. Mineral control and physico-chemical conditions (e.g., Eh and pH) probably had effective roles in the behavior of elements during weathering. Based on the concentration of trace 1

Journal Pre-proof elements, such as Zr, Cr, and Ga, and the conservative elemental indices (e.g., Sm/Nd, Ti/Zr, and Nb/Ta), the basaltic rocks were a plausible source rock for the Amir-Abad karst-type bauxite deposit.

Keywords: Amir-Abad karst-type bauxite; Mass balance; Chemical Index of Alteration; Parental affinity; Northwestern Iran

1. Introduction

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Bauxites are weathered aluminum-deposits formed through the weathering of parent rocks rich in

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aluminosillicates in tropical to inter-tropical regions (30° north latitude and 30° south latitude) under warm and humid climatic conditions. Despite the major source of Al, bauxites contain a group of trace elements, including

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the high-field strength elements (HFSE; Ti, P, Zr, Nb, and the rare earth elements/REE), Ni, Cr, Co, V, Sc, and

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Ga, as well as Au (Mongelli et al., 2014; Ahmadnejad et al., 2017; Gamaletsos et al., 2017, 2019; Khosravi et al.,

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2017; Radusinović et al., 2017; Ling et al., 2018; Abedini et al., 2019; Ellahi et al., 2019). On the basis of the bedrock lithology, they are categorized into lateritic and karstic bauxites (Bárdossy, 1982). There is no genetic

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relationship between the karstic bauxites and their underlying carbonates, and they show a wide range from autochthonous to allochthonous in origin. In contrast, the lateritic bauxites are genetically associated with the

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underlying alumosilicate rocks of igneous, sedimentary, or metamorphic origins.

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Based on the global geographical classification for bauxites (Bárdossy, 1982), bauxite deposits in Iran belong to the Irano–Himalayan bauxite belt, and are similar to those from the Mediterranean bauxite belt. They are Permian, Permo–Triassic, Triassic, Triassic to Jurassic, and Cretaceous in age, and are spatially distributed in four structural zones, namely northwestern Iran, the Alborz Mountains, the Zagros Simply Folded Belt (ZSFB), and the Central Iranian Plateau (CIP) (Ahmadnejad et al., 2017; Khosravi et al., 2017; Abedini et al., 2018, 2019; Ellahi et al., 2019; see Fig. 1a). The Cretaceous Bauxite deposits mainly occur in the ZSFB, whereas the Permian and Permo–Triassic bauxite deposits have chiefly been reported from northwestern Iran (see Fig. 1a). Some studies have recently been focused on bauxite deposits from northwestern Iran in order to constrain the parental affinity of bauxites, to evaluate the autochthonous or allochthonous origin of the Permian and Permo– 2

Journal Pre-proof Triassic bauxites, to reveal effective factors controlling the distribution and mobility of trace elements, and to evaluate the depositional condition of bauxites (e.g., Khosravi et al., 2017; Abedini et al., 2018, 2019). So far, no comprehensive studies have been carried out on the Triassic–Jurassic bauxite deposits in northwestern Iran. We studied one of these deposits with the aim of determining the behavior of various elements, especially for trace elements, during weathering processes and mass change calculations, environmental conditions of the weathering (e.g., Eh-pH, drainage, and palaeo-climate), and the parental affinity of ores.

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2. Geological background

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During the Triassic to Jurassic periods, closure of the Palaeo-Tethys Ocean was coincident with subduction of the Neo-Tethys oceanic lithosphere beneath the Eurasia (Berberian and Berberian, 1981). During

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the Lower Triassic marine trangression, thick dolomitic limestones of the Elika Formation were deposited in the

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CIP, Alborz Mountains, and northwestern Iran. Following movement of the Afro–Arabian plate toward the

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Eurasia, the CIP and Alborz Mountains were located in the tropics during the Triassic to Jurassic times (Berberian, 1983). Formation of carbonate units of the Elika Formation is one of the principle features of the

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Tethys basins. Progressive sea-level fall resulted in the development of a sabkha enviroment during the Middle Triassic age, which was followed by epeirogenic movements and the subaerial exposure of the Triassic

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dolomites of the Elika Formation (Esmaeily et al., 2010). The Elika karstified carbonates host bauxite deposits in

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the Alborz Mountains and some parts of the ZSFB and northwestern Iran. These carbonates were finally overlain by the Lower Jurassic Shemshak Formation and the other younger units. During the Late Triassic (Early Cimmerian) age, compressional movements in northern and central Iran were followed by extensional movements (Esmaeily et al., 2010). The initiation of these extensional movements coincided with eruptions of andesitic–basaltic lava flows (Berberian and King, 1981), but continued into the lower parts of the Shemshak Formation. The Middle Triassic (Early Cimmerian) eroded and karstified carbonates were overlain by the Late Triassic andesitic–basaltic rocks (Annells et al., 1975). The Amir-Abad bauxite deposit is located 8 km of south of Maragheh city, East-Azarbaidjan province, Iran (see Fig. 1a). The Triassic dolomitic limestone of the Elika Formation and the Lower Jurassic sandstone, 3

Journal Pre-proof siltstone, shale, and coal of the Shemshak Formation are the oldest rocks in the Amir-Abad area. The Middle Jurassic marly limestones of the Dalichay Formation were overlain by the Late Jurassic limestone and dolomitic limestone of the Lar Formation and the Cretaceous limestone of the Tizkuh Formation (see Fig. 1b). Scattered basalts are embedded in the carbonate of the Elika Formation (see Fig.1a). The bauxite ores occur as layershaped and lenticular pockets in the contact of the dolomitic limestone of the Elika Formation and the sandstone, shale, and coal of the Shemshak Formation. Eight bauxitic horizons have been recognized with NW–SE, N–S, and NE–SW trends, variable thicknesses between 3 and 22 m, and a total length of about 2.5 km. The formation

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of the bauxite ores in depressions of the carbonate footwall, karstified bedrocks, and sharp contact between the

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bauxite horizons and the dolomitic limestone bedrocks of the Elika Formation are characteristic geological

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features of this deposit.

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3. Sampling and methods

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A profile perpendicular to the trend of one of the bauxite profiles was selected for detailed mineralogical and geochemical studies (see Fig. 1b). The bauxite ores were deposited in karstic depressions of the carbonate

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footwall of the Elika Formation, and categorized into two subsets, on the basis of physical characteristics (e.g., surface color, hardness, and texture). A total of twenty representative samples were collected at intervals of

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about 1 m from the bottom to the top of the profile according the following scheme: R-1 to R-9 are of brownish

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red ores (BRO) and R-10 to R-20 of red ores (RO) (see Fig. 2). Likewise, seven representative samples from the basalts within the carbonate rocks of the Elika Formation (4#) and the dolomitic limestone of the Elika Formation (3#) were chosen for geochemical analysis. Approximately 0.25 gram of the powered samples was digested by fusion with lithium tetraborate and lithium meta-borate, and heated in an oven at 1000 °C. After cooling, nitric acid was added to the main solution and diluted 100 mL. Major and trace elements (including REE) were analyzed at the Activation Laboratories Ltd (ALS Chemex, Canada) by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP–AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP–MS), respectively. Precisions are generally better than 5%

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Journal Pre-proof for most elements. The loss on ignition (LOI) content was obtained by measuring the weight loss of 1 gram of the sample after 90 min of heating at 950 °C. In order to determine whole-rock mineralogical composition, twenty bauxite ores were ground to 200mesh using agate jars and agate milling balls. The bulk mineralogical composition was determined by means of powder X-ray diffraction (PXRD) using a Siemens D5000 X-ray diffractometer at the Geological Survey of Iran, Tehran under the following conditions: Cu-Kα radiation, 40 kV, 30 mA, scanning speed 8° per minute, and scan range 2°–60°. Microscopic studies were carried out on polished thin sections from the bauxite ores with the aim

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of identifying textural features at the Department of Geology at Urmia University, Iran using Olympus BX60F5

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optical microscope. Mineralogy at the microscale was checked by scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDS). SEM-EDS analysis was utilized at the Razi Metallurgical

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Research Center, Iran using a Hitachi S-3400N SEM equipped with a Link Analytical Oxford IE 350 energy

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dispersive X-ray spectrometer (EDS). Analytical operation condition was 15 kV-accelerating voltage, 1 nA-

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beam current, and 1 µm-beam diameter.

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4. Results 4.1. Textural and mineralogical features

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Hematite, which occurs as spherical components, is the major mineral phase in the bauxite ores

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identified by optical microscopic observations. Ooidic, pisoidic, spastoidic, and round-grained textures were observed both in the BRO and in the RO (Figs. 3a–d). According to Bárdossy (1982), the presence of ooidic, pisoidic, and spastoidic textures in the bauxite ores indicates an autochthonous origin for the Amir-Abad karsttype bauxite, and can be attributed to the heterogeneity of colloids derived from the parent rock through weathering processes (Gu et al., 2013). Whereas, the presence of round-grained texture implies an allochthonous origin for the bauxite ores. It suggests that the Amir-Abad deposit was formed initially by "in-situ" weathering from the parent rock, and after transportation deposited in karstic depressions of the carbonate footwall in the current locations. On the basis of the PXRD analyses, there is no significant difference in mineral assemblages of the bauxite ores. Based upon the results of mineralogical analysis, hematite, diaspore, and kaolinite group 5

Journal Pre-proof minerals are the dominant constituent phases of the bauxite ores, and rutile and goethite occur as minor phases (Table 1 and Fig. 4a and b). Hematite is the main iron oxide in the Amir-Abad bauxite ores. This mineral can be generated by the decomposition of primary Fe-bearing constituents of the parent rock, and concentrated under suitable Eh-pH conditions, and/or by dehydration of goethite under tropical climates (Bárdossy and Aleva, 1990). The presence of both hematite and goethite in the bauxite ores suggests that dehydration of goethite probably did not occur completely at Amir-Abad. Based on the SEM-EDS analyses, kaolinite, montmorillonite, goethite, and hematite were identified in the BRO (Fig. 5a), whereas zircon, diaspore, and rutile/anatase were

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present in the RO (Fig. 5b and c). Accessory minerals, such as zircon and rutile/anatase were not detected by

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PXRD, probably due to low concentration of these minerals in the bauxite ores. Hematite is sometimes

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surrounded by a kaolinite matrix, as shown in Fig. 5a, suggesting leaching conditions in a well-drained system.

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4.2. Geochemistry

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4.2.1. Geochemistry of the major elements

The results of whole-rock analysis of major and trace elements (including REE), along with selected

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elemental ratios from the representative samples of the bauxite ores, the basalts, and the dolomitic limestones of the Elika Formation are presented in Tables 2 and 3, respectively. Al (Al2O3: 28.9–51.2 wt.%), Si (SiO2: 13.7–

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32.0 wt.%), and Fe (Fe2O3: 14.7–24.2 wt.%) are the major elements of the Amir-Abad bauxite ores, and their

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oxides show a wide range of variations in content. Other elements, such as Ca (CaO: 0.0–0.3 wt.%), Na (Na2O: 0.0–0.1 wt.%), K (K2O: 0.0–0.3 wt.%), Mg (MgO: 0.0–0.1 wt.%), Mn (MnO: 0.1–0.5 wt.%), and P (P2O5: 0.1– 0.2 wt.%) are present in low contents in the bauxite ores. However, CaO, Na2O, K2O, MgO, Fe2O3, and P2O5 show a more enrichment in the lower parts of the profile (the BRO) than the upper parts (the RO) (see Table 2). In contrast, high Al2O3 concentrations are present in the RO. Ca (CaO: 43.1–43.2 wt.%) is the major element of the dolomitic limestones of the Elika Formation, whereas Si (SiO2: 49.7–51.4 wt.%), Al (Al2O3: 13.2–13.7 wt.%), and Fe (Fe2O3: 12.2–13.7 wt.%) are the major elements in the basalts (see Table 2).

4.2.2. Geochemistry of the trace elements 6

Journal Pre-proof Zr displays the highest concentrations among the distinct HFSE (i.e., U, Th, Hf, Zr, Nb, and Ta), ranging from 324 to 645 ppm. All HFSE have higher concentrations in the RO relative to the BRO. Large-ion lithophile elements, including Ba, Sr, and Rb, in comparison with Cs display wide variations in content. Barium, Sr, and Rb concentrations generally increase downward toward the BRO, with an exception in sample R-16. Barium, Sr, Rb, and Cs concentrations in the bauxite ores range from 16–222 ppm Ba (average 110 ppm), 20–288 ppm Sr (average 145 ppm), 8–110 ppm Rb (average 53 ppm), and 0–8 ppm Cs (average 4 ppm). Concentrations of distinct transition metals, including Ni, Cr, Co, Sc, Y, and V in the bauxite ores range from 118–408 ppm Ni,

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604–747 ppm Cr, 164–289 ppm Co, 28–52 ppm Sc, 29–105 ppm Y, and 583–916 ppm V (see Table 2). High

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Concentrations of Ni, Cr, and Co are observed in the BRO, and high concentrations of V and Sc occur in the RO. Light REE (ΣLREE; La–Eu), heavy REE (ΣHREE; Gd–Lu), and ΣREE (La–Lu) concentrations in the

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Amir-Abad representative ores range from 122–897 ppm (average 384 ppm), 20–66 ppm (average 44 ppm), and

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151–933 ppm (average 428 ppm), respectively (see Table 3). REE concentrations in the basalts and the dolomitic

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limestones of the Elika Formation are 89–162 ppm and 14–28 ppm, respectively. The (LREE/HREE)N, (La/Yb)N, and La/Y ratios, reflecting fractionation of LREE from HREE, in the bauxite ores along the profile are

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1.1–14.2 (LREE/HREE)N, 1.5–40.0 (La/Yb)N, and 0.2–4.6 La/Y (see Table 3). The range of these ratios in the basalts and the dolomitic limestone of the Elika Formation is 2.4–3.2 and 3.5–9.3 (LREE/HREE)N, 4.3–7.1 and

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5.1–14.4 (La/Yb)N, and 0.6–0.9 and 0.5–1.4 La/Y, respectively. The range of Eu and Ce anomalies in the Amir-

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Abad bauxite ores is 0.5–1.0 (average 0.8) and 0.7–1.9 (average 1.2), respectively. These anomalies in the basalts and the dolomitic limestone of the Elika Formation range from 0.4–0.8 and 0.7–0.8 (Eu/Eu*), and 0.9– 1.0 and 2.0–2.4 (Ce/Ce*). On the basis of some characters (e.g., CIA, Eu/Eu*, Ce/Ce*, La/Y, (La/Yb)N, (ΣLREE/ΣHREE)N, origin, and parent rock), a comparison of the Amir-Abad bauxite deposit with some wellknown bauxite deposits in the world (e.g., China, Italy, Yugoslavia, India, Africa, Spain, Greece, and Iran) is presented in Table 4. Regardless origin and parent rock, the Amir-Abad deposit is significantly different from other deposits.

5. Discussion 7

Journal Pre-proof 5.1. The Chemical Index of Alteration At a regional or global scale, the weathering indices (e.g., Chemical Index of Alteration, CIA; Nesbitt and Young, 1982) provide invaluable insights into the degree of alteration of weathered materials, the weathering condition of source regions for the ancient and modern sediments, and the behavior of mobile and immobile elements during weathering. The CIA was calculated as [Al2O3/(Al2O3 + CaO* + Na2O + K2O)] × 100. CaO* is the amount of CaO incorporated in silicate fraction of the sample measured. The CIA values represent the decomposition of primary rock-forming minerals (e.g., K-feldspar) of the precursor rock and the release of

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labile elements, such as Ca, Na, and K relative to Al which is assumed to be immobile (Babechuk et al., 2014).

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As shown in Fig. 6a, values of the CIA in the bauxite ores range from 96.8 to 99.7 (average 98.6), indicating

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5.2. Geochemical indices and REE distribution patterns

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nearly complete removal of mobile elements during the formation of the Amir-Abad bauxite deposit.

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Variations of the La/Y ratio in bauxites represent pH variations in weathering solutions; thus values of La/Y> 1 and La/Y< 1 indicate basic and acidic environments, respectively (Maksimović and Panto, 1991).

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Values of this ratio in the representative bauxite ore samples range from 0.2 to 4.6 (Table 3 and Fig. 6b), indicating a basic environment in the basal parts (R-1 to R-12) close to the carbonate bedrock, and an acidic

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environment in the upper parts of the profile (R-13 to R-20). The (La/Yb)N ratio in the karst-type bauxites is also

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controlled by pH fluctuations in soil solution (Mongelli et al., 2014); lower (La/Yb) N ratios indicate more acidic conditions. The (ΣLREE/ΣHREE)N and (La/Yb)N ratios in the top half of the selected profile (0–10 m; 1.1–6.0 and 1.5–10.1, respectively) are significantly lower than the lower half of the profile (10–20 m; 4.0–14.2 and 8.7– 40.0, respectively; Table 3 and Fig. 6b). The bauxite ores along the selected profile display an irregular pattern of Eu and Ce anomalies (see Fig. 6c). However, the ores in the upper parts of the profile (the RO) have more positive Ce and negative Eu anomalies than those in the basal parts (the BRO). In the chondrite-normalized REE distribution diagram, the Amir-Abad bauxite ores are characterized by weakly concave and downward trends, together with negative Eu anomalies (see Fig. 7). The same REE patterns for the bauxite ores probably reflect a homogeneous parent rock from which the Amir-Abad karstic bauxite was 8

Journal Pre-proof derived under humid, subtropical climates. Enrichment of LREE compared to HREE toward the lower parts of the profile is consistent with variations of the La/Y, (ΣLREE/ΣHREE)N, and (La/Yb)N ratios across the profile in Fig. 6b.

5.3. Mass balance calculations During weathering and bauxitization processes, Ti, Al, Hf, Zr, Nb, Ta, Ga, Sc, Y, V, and Th have generally been considered as less mobile elements, due to their high preservation against physico-chemical

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phenomena in the near-surface environment (MacLean et al., 1997; Calagari and Abedini, 2007; Mameli et al.,

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2007; Gu et al., 2013; Mongelli et al., 2014). These elements have generally been used to evaluate chemical modifications and mass balances of bauxites during weathering (Ling et al., 2017, 2018, and references therein).

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Mass balance calculation is commonly used to quantify the changes in elemental concentrations during

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weathering, and can be considered as an effective means of evaluation the relative depletion/enrichment of

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elements relative to an element assumed to be less mobile (MacLean et al., 1997). This calculation is applicable to bauxite deposits (MacLean et al., 1997; Khosravi et al., 2017; Ling et al., 2018; Abedini et al., 2019).

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Depletion/enrichment of elements in bauxites during weathering depends on a series of factors. These include the nature of precursor rocks, physico-chemical and climatic conditions of the weathering environment, chemical

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properties of elements, related carrier mineral phases, and biological activity associated with the deposit, as well

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as the duration and intensity of weathering and drainage. During weathering processes, physico-chemical conditions (e.g., pH and oxidization-reduction condition) have an effective role in the mobility of elements (Maksimović and Panto, 1991), and also in the elemental composition of bauxites (Mordberg, 1996). In this study, TiO2 has a highly positive correlation (≥0.92) with the other immobile elements, such as Al, Zr, and Nb (see Fig. 8). Thus, Ti is the most suitable immobile element for mass balance calculations. Taking into account Ti as a less mobile element and the Upper Continental Crust (UCC; Taylor and McLennan, 1985) as a parental material of the bauxite ores, the relative mobility of elements was calculated by the AWI method ([(X bauxite ore/Ti bauxite ore)

/ (X UCC/Ti UCC) – 1] × 100; Nesbit, 1979); X is concentration of the selected element.

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Journal Pre-proof 5.3.1. Behavior of the major and selected trace elements during bauxitization Silica incorporated in the phyllosilicates (e.g., the kaolinite group minerals) can be released into solution during the earlier stages of bauxitization under humid, tropical climates (Babechuk et al., 2014). Fluctuations of the groundwater table, abundant rainfall, and a short drier season favor a deep chemical weathering and pedogenesis, and desilification (Bárdossy and Aleva, 1990). Iron is poorly soluble, and can form secondary mineral phases. Indeed, the behavior of Fe strongly depends on the redox and drainage conditions of the weathering environment (Babechuk et al., 2014). Iron is more concentrated in the lower parts (the BRO) than the

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upper parts of the profile (the RO; Fig. 9a), corresponding to variations of the (ΣLREE/ΣHREE)N, (La/Yb)N, and

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La/Y ratios along the profile in Fig. 6b. Leaching of Fe from the top to the bottom across the selected profile corresponds to an increase in ferruginous phases in a downward direction across the profile. Oxidation of

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organic matter, favoring acidic conditions promotes the mobilization of Fe from primary Fe-bearing minerals of

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the parent rock, as soluble Fe2+ ion (Mameli et al., 2007; Ling et al., 2015, 2017) through organometallic

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complexes (Esmaeily et al., 2010). Aluminum shows a minor change along the Amir-Abad bauxite profile, thus can be regarded as a less mobile element (Fig. 9a). Depletion of P throughout the selected profile probably

9a).

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represents the decomposition of P-bearing minerals (e.g., apatite) of the parent rock during weathering (see Fig.

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As with Fe, Ni, Cr, and Co were leached from the upper parts of the profile by acidic percolating

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solutions, and concentrated toward the carbonate bedrock under alkaline conditions (see Fig. 9b). Concentration of Ni and Co in bauxites may be controlled by adsorption mechanism by Fe-oxyhydroxides (Mongelli et al., 2014; Radusinović et al., 2017). Thus, the presence of Fe-oxyhydroxides and alkaline conditions in the lowermost parts of the weathered profile can be considered the principle factors controlling the concentration of Ni and Co in the basal parts of the profile (the BRO). Niobium, Ga, and Ta show minor changes across the selected profile during weathering (see Fig. 9b), suggesting that they were less mobile during the formation of the Amir-Abad bauxite from the alumosilicate-rich parent rock. Gallium tends to be concentrated in diaspore, but not in Fe-phases (Gamaletsos et al., 2019) during the later stages of bauxitization (Bárdossy and Aleva,

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Journal Pre-proof 1990; Mongelli et al., 2014; Ling et al., 2018), due to the similarities of geochemical and crystal-chemical properties of Ga and Al (Ling et al., 2018, and references therein; Gamaletsos et al., 2019). High leaching of alkali and alkaline earth metals (e.g., Na, K, Rb, Cs, Ca, Mg, Sr, and Ba) (see Fig. 9c) and Si reflect a good drainage, the decomposition of primary silicates (e.g., K-feldspar, plagioclase, mica, pyroxene, and hornblende) of the parent rock through the reaction of these minerals with solutions during weathering (Beyala et al., 2009), and their inabilities to form stable secondary mineral phases (Giorgis et al., 2014). HFSE, such as Hf, Zr, Nb, Ta, and Th have similar chemical properties. They are relatively stable during

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bauxitization, and would tend to be concentrated in the accessory minerals, such as zircon and anatase (Calagari

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and Abedini, 2007; Mameli et al., 2007; Mongelli et al., 2014; Gamaletsos et al., 2019). Highly positive correlation of TiO2 and distinct HFSE, such as Th (0.84), Nb (0.95), Ta (0.86), and Zr (0.93), which are in line

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with the previous studies (e.g., Gamaletsos et al., 2011), and the presence of solid mineral phases, such as

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anatase/rutile and zircon in the bauxite ores can be considered important agents of high stability and the

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conservative behavior of these elements to weathering in this study. Periodic subaerial exposure in a tropical climate favors ferrallitization processes (Yuste et al., 2015). Enrichment of V may be related to ferrallitization

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(Yuste et al., 2017) and its substitution in Fe-bearing phases, due to similar charge and ionic radius of V and Fe. Although V tends to be adsorbed on Fe-oxyhydroxides, the intensity of adsorption depends on the pH of the

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weathering environment (McKenzie, 1980). Vanadium was leached from the upper and middle parts of the

(Fig. 9d).

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profile by acidic percolating solutions, and concentrated toward the carbonate bedrock under alkaline conditions

5.3.2. Distribution and fractionation of REE during bauxitization Water-rock interaction (e.g., sedimentation-diagenesis and, principally, chemical weathering) under different Eh and pH conditions plays a critical role in REE fractionation (Nesbitt, 1979; Ling et al., 2018). Weathering of constituent phases of the parent rock results in the mobilization of elements, and also fractionation of LREE and HREE, as well as Eu and Ce anomalies (MacLean et al., 1997; Karadag et al., 2009; Gu et al., 2013). Distribution and fractionation of REE in bauxites depends on the chemical composition of 11

Journal Pre-proof parent rocks, fluctuations in soil solution pH, the presence of organic and inorganic ligands in the soil, ionization potential of REE, microbial activity, and the stability of primary REE-bearing and secondary minerals (Cantrell and Byrne, 1987; Braun et al., 1998; Karadag et al., 2009; Esmaeily et al., 2010; Mongelli et al., 2014; Ahmadnejad et al., 2017; Yuste et al., 2017; Ling et al., 2018). Negative Eu anomalies of the representative ore samples (0.5–1.0; Fig. 6c) probably reflect the preferential decomposition of primary Eu-bearing minerals (i.e., calcic plagioclase) of the parent rock during the formation of the Amir-Abad deposit. A cerium anomaly has been considered as a potentially valuable tool for

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identifying different geological conditions and/or processes (e.g., Mongelli et al., 2014). In detail, a succession

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of varying periods of weathering intensity and redox conditions of the soil environment lead to fluctuations of Ce anomaly, corresponding to the climatic changes (Braun et al., 1998). Cerium fractionation in the uppermost

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parts of the karst-type bauxite deposits has previously been reported from several bauxites of the Mediterranean

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bauxite province (e.g., Maksimović and Panto, 1991; Radusinović et al., 2017; Gamaletsos et al., 2019). During

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weathering processes, Ce in the form of Ce4+ can be absorbed by kaolinite group minerals, either as a monomeric species or as a polymeric hydroxication (Boulange et al., 1990). Positive Ce anomalies in the upper parts of the

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profile may be related to the presence of cerianite (CeO2), a result of the oxidation of Ce3+ into the less mobile Ce4+ (Karadag et al., 2009; Gu et al., 2013; Mongelli et al., 2014; Gamaletsos et al., 2019, and references

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therein). On the other hand, positive Ce anomalies of the ores are in agreement with a clayey environment

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developed from weathering processes, due to selective adsorption of Ce ions onto clay particles. The REE fractionation patterns can be utilized as a valuable tool for the reconstruction of landscape evolution and palaeo-environmental conditions (Marker and Oliveira, 1994). REE are mobilized or fractionated by a number of mechanisms related to redox conditions of the weathering environment. They tend to be variably mobile under acidic conditions by solutions percolating downward; however, their mobility decrease under neutral to alkaline conditions (Nesbitt, 1979; Karadag et al., 2009; Gu et al., 2013). In addition, REE would mobilize and fractionate under humid, tropical to subtropical climates during intensive chemical weathering and strong drainage conditions (Meshram and Randive, 2011, and references therein). At Amir-Abad, the bauxite ores with La/Y< 1 (R-13 to R-20) have higher CIA values than those with La/Y> 1 (R-1 to R-12) (see Fig. 6a 12

Journal Pre-proof and b). This attribute is consistent with variations of the (ΣLREE/ΣHREE)N and (La/Yb)N ratios along the entire profile. As shown in Fig. 9e, LREE were leached from the uppermost parts, and concentrated in the lowermost parts of the profile. In contrast, HREE exhibit an irregular pattern. This finding is consistent with the point that LREE are more efficiently adsorbed onto the secondary solid phases than HREE, as the pH of the weathering environment increases (Pourret et al., 2010, and references therein). It seems that an increasing abundance of Feoxyhydroxides downward toward the carbonate bedrock probably controlled re-distribution of REE across the profile, especially LREE. In addition to the pH effects and the pH-controlled adsorption/precipitation of LREE

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to Fe-oxyhydroxides, depletion-enrichment patterns of HREE and, mainly, LREE in Fig. 9e can be related to

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chelation to organic ligands in the uppermost parts of the profile, followed by their precipitation toward the carbonate bedrock, in which organic ligands are less abundant (Lara et al., 2018, and references therein). The

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presence of organic matter and an acidic environment in the uppermost parts of the profile, and mineral control

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can be considered as effective agents of REE fractionation in the bauxite ores at Amir-Abad.

5.4. Parental affinity

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In spite of many mineralogical and geochemical studies on bauxites worldwide, the determination of provenance of the karst-type bauxite deposits, especially in allochthonous bauxites, is debatable, because of the

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intensity of mechanical and chemical weathering, and the mobilization of many elements (Bárdossy, 1982;

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MacLean et al., 1997; Calagari and Abedini, 2007). It is thought that the majority of bauxite deposits are directly related to the underlying source rocks (Bárdossy and Aleva, 1990). However, carbonate rocks, in most cases, do not have sufficient potential to generate bauxites, due to the lack of primary rock-forming minerals (e.g., Mameli et al., 2007; Mondillo et al., 2011, and references therein; Mongelli et al., 2014; Khosravi et al., 2017; Abedini et al., 2019). Distribution of immobile elements and their ratios are a powerful tool in evaluating the genetic history of the karst-type bauxites from the Mediterranean area (Maksimović and Panto, 1991; MacLean et al., 1997; Mameli et al., 2007) and in identifying the precursor rock of bauxites (MacLean et al., 1997; Calagari and Abedini, 2007; Gu et al., 2013; Khosravi et al., 2017; Ling et al., 2018; Abedini et al., 2019). Likewise, the 13

Journal Pre-proof Sm/Nd ratio has been used to constrain the parental affinity of bauxites (Babechuk et al., 2014; Mongelli et al., 2014; Khosravi et al., 2017; Abedini et al., 2019), because only a minor fractionation of Sm and Nd occurs during weathering processes (Viers and Wasserburg, 2004). According to the Zr–Ga–Cr ternary diagram of Özlü (1983), the Amir-Abad bauxite ores plot within and close to the field of mafic precursor rock (Fig. 10). In order to further determine the parental affinity of the Amir-Abad bauxite ores, bivariate plots of TiO2 versus Zr and Sm/Nd versus Ti/Zr and Nb/Ta were used. There is a good and positive correlation between TiO2 and Zr (0.93) in the bauxite ores (Fig. 11a). The weathering line passes through data points of the representative samples of the

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basalt, pointing to a genetic relationship between the bauxite ores and the basalts within the carbonate of the

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Elika Formation. According to Fig. 11b and c, the Amir-Abad bauxite ores are also distinctly remote from the dolomitic limestones of the Elika Formation, but plot close to the basalts. These diagrams may support the idea

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that mafic rock of basaltic composition, most likely related to volcanic activities in the Iranian platform during

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the Triassic age, was a possible precursor of the Amir-Abad bauxite ores, similar to the Permian and Permo–

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Triassic bauxite deposits in northwestern Iran (e.g., Darzi-Vali in Table 4; Khosravi et al., 2017, and references therein). This finding is consistent the fact, as previously noted in the literature, that the dissolution of carbonate

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6. Conclusions

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rocks is not a common mechanism for the formation of bauxites.

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1- The Amir-Abad karst-type bauxite deposit is characterized by ooidic, pisoidic, spastoidic, and round-grained textures. The bauxite ores are sandwiched between the dolomitic limestone of the Elika Formation and the sandstone, siltstone, shale, and coal of the Shemshak Formation, and mainly consist of hematite, diaspore, and kaolinite group minerals (e.g., kaolinite and montmorillonite), with lesser amounts of goethite, anatase/rutile, and zircon. 2- Negative Eu anomalies of the bauxite ores probably indicate the decomposition of calcic plagioclase of the parent rock during weathering. Positive Ce anomalies in the upper parts of the profile may be related to the presence of cerianite and/or adsorption of Ce ions onto clay particles.

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Journal Pre-proof 3- The bauxite ores with La/Y< 1 (R-13 to R-20) have higher CIA values than those with La/Y > 1 (R-1 to R12). 4- As weathering advanced, Si, P, and alkali and alkaline earth metals (e.g., Na, K, Rb, Cs, Ca, Mg, Sr, and Ba) were almost completely leached across the profile, whereas Fe, Ni, Co, Cr, V, and REE were depleted from the upper parts, and re-precipitated and accumulated toward the carbonate bedrock. However, Al, Nb, Ga, Ta, Th, Hf, and Zr showed only a minor change across the weathered profile with respect to Ti, probably due to their low mobility during weathering.

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5- Oxidation of organic matter in the uppermost parts of the profile promoted an acidic environment, which

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favors the preferential leaching of mobile elements from primary rock-forming minerals of the precursor rock. 6- Based on the concentration of trace elements, such as Zr, Cr, and Ga and bivariate plots of TiO2 versus Zr and

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Sm/Nd versus Ti/Zr and Nb/Ta, the basaltic rocks within the carbonate of the Elika Formation were the most

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plausible source rock for the Amir-Abad karst-type bauxite deposit.

Acknowledgments

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The project was supported by the Bureau of Research Affairs of Urmia University, to which we are grateful. Our gratitude is further expressed to Professor Stefano Albanese and Associate Editor for their advices, valuable

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suggestions, and editorial assistance, and also two anonymous reviewers for reviewing and making critical

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comments on this manuscript. The authors express their gratitude to Professor P. Davidson at ARC Centre of Excellence in Ore Deposits, University of Tasmania, Australia, for English editing of the final version of the manuscript.

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Bárdossy, G., Aleva, G.J.J., 1990. Lateritic bauxites. Developments in Economic Geology, vol. 27. Elsevier Scientific Publication, Amsterdam, pp. 1–624.

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Ling, K.Y., Zhu, X.Q., Tang, H.S., Li, S.X., 2017. Importance of hydrogeological conditions during formation of

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the karstic bauxite deposits, Central Guizhou Province, southwest China: a case study at Lindai deposit. Ore

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Ling, K.Y., Zhu, X.Q., Tang, H.S., Wang, Z.G., Yan, H.W., Han, T., Chen, W.Y., 2015. Mineralogical

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characteristics of the karstic bauxite deposits in the Xiuwen ore belt, central Guizhou province, southwest China. Ore Geol. Rev. 65, 84–96. Long, Y., Chi, G., Liu, J., Jin, Z., Dai, T., 2017. Trace and rare earth elements constraints on the sources of the Yunfeng paleo-karstic bauxite deposit in the Xiuwen–Qingzhen area, Guizhou, China. Ore Geol. Rev. 91, 404–418. MacLean, W.H., Bonavia, F.F., Sanna, G., 1997. Argillite debris converted to bauxite during karst weathering: evidence from immobile element geochemistry at the Olmedo Deposit, Sardinia. Miner. Deposita 32, 607– 616.

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Journal Pre-proof Maksimović, Z., Panto, G.Y., 1991. Contribution to the geochemistry of the rare earth elements in the karstbauxite deposits of Yugoslavia and Greece. Geoderma 51 (1–4), 93–109. Mameli, P., Mongelli, G., Oggiano, G., Dinelli, E., 2007. Geological, geochemical, and mineralogical features of some bauxite deposits from Nurra (Western Sardinia, Italy): insights on conditions of formation and parental affinity. Int. J. Earth Sci. 96 (5), 887–902. Marker, A., Oliveira, J.J., 1994. Climatic and morphological control of rare earth element distribution in weathering mantles on alkaline rocks. Catena 21 (2–3), 179–193.

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Italy): chemical fractionation and parental affinities. Ore Geol. Rev. 63, 9–21. Mordberg, L.E., 1996. Geochemistry of trace elements in Paleozoic bauxite profiles in northern Russia. J.

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Nesbitt, H., Young, G.M., 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 299 (5885), 715–717. Nesbitt, H.W., 1979. Mobility and fractionation of rare earth elements during weathering of a granodiorite. Nature 279, 206–210. Özlü, N., 1983. Trace-element content of “karst bauxites” and their parent rocks in the Mediterranean belt. Miner. Depos. 18 (3), 469–476. Pourret, O., Gruau, G., Dia, A., Davranche, M., Molénat, J., 2010. Colloidal control on the distribution of rare earth elements in shallow groundwaters. Aquatic Geochem. 16, 31–59.

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bauxite: an example from the Lower Cretaceous of NE Spain. Ore Geol. Rev. 84, 67–79.

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Journal Pre-proof Figure captions Fig. 1. (a) The spatial distribution of bauxite deposits in four structural divisions of Iran. The position of the Amir-Abad bauxite deposit is marked by a red quadrangle. (b) Simplified geological map of the Amir-Abad deposit located on the contact of the dolomitic limestone of the Elika Formation, and the sandstone, siltstone, shale, and coal of the Shemshak Formation.

Fig. 2. Cross section (a) and stratigraphic column (b) of the selected profile in the Amir-Abad bauxite deposit

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(refer to Fig. 1b for position and strike of the selected profile). The positions of the representative bauxite ore

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samples are marked by the filled circles. (c) Hand specimens of the BRO (R-6) and RO (R-16).

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Fig. 3. Optical microscopy of the bauxite ores at Amir-Abad: (a) pisoidic texture in the BRO; (b) ooidic texture

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in the BRO; (c) spastoidic texture in the RO; (d) round-grained texture in the RO. All photos are in reflected

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light. Abbreviation: Hem = hematite (Whitney and Evans, 2010).

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Fig. 4. Powder-XRD patterns of the bauxite ores in the BRO and RO from the Amir-Abad deposit.

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(Whitney and Evans, 2010).

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Abbreviations: Dsp = diaspore, Gth = goethite, Hem = hematite, Kln = kaolinite group minerals, Rt = rutile

Fig. 5. SEM-EDS results showing: (a) hematite, goethite, kaolinite, and montmorillonite in the BRO; (b) zircon in the matrix of diaspore in the RO; (c) rutile/anatase in the RO. Abbreviations: Dsp = diaspore, Gth = goethite, Hem = hematite, Kln = kaolinite, Mnt = montmorillonite, Rt/Ant = rutile/anatase, Zrn = zircon (Whitney and Evans, 2010).

Fig. 6. Variations of the CIA (a), (ΣLREE/ΣHREE)N, (La/Yb)N, and La/Y (b), and Eu/Eu* and Ce/Ce* (c) along the Amir-Abad selected profile.

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Journal Pre-proof Fig. 7. Chondrite-normalized REE spider diagram for the representative bauxite ore samples from Amir-Abad.

Fig. 8. Binary diagrams showing correlation between TiO2 (wt.%) and trace elements Zr and Nb (ppm), and Al2O3 (wt.%).

Fig. 9. Percentage deviation of elements relative to Ti with regard to the UCC as a parental material of the AmirAbad bauxite ores for (a) Al, P, Si, and Fe, (b) Ni, Cr, Co, Nb, Ga, and Ta, (c) Rb, Ba, Cs, and Sr, (d) U, Th, Hf,

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Zr, Y, and V, and (e) LREE and HREE.

Fig. 10. Ternary plot of Zr–Ga–Cr (Özlü, 1983) for the Amir-Abad bauxite ores. A, B, C, and D (the asterisked)

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represent the concentration of Zr, Cr, and Ga in acidic, intermediate, basic, and ultrabasic igneous rocks,

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respectively. The numbers I, II, III, and IV represent the area of influence of ultramafic, mafic, intermediate

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(argillaceous), and acidic igneous precursor rocks, respectively.

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Fig. 11. Bivariate plots of TiO2–Zr (a), Sm/Nd–Ti/Zr (b), and Sm/Nd–Nb/Ta (c), suggesting the basalt within the

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carbonate of the Elika Formation as a plausible protolith for the Amir-Abad bauxite ores.

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Journal Pre-proof Table 1- Results of PXRD analyses for twenty ore samples of the Amir-Abad deposit.

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Minor phases Goethite, rutile, kaolinite group minerals Goethite, rutile, kaolinite group minerals Rutile Rutile Hematite, goethite, rutile Goethite, rutile Goethite, rutile Rutile Rutile Rutile Rutile Rutile, goethite Hematite, goethite Hematite Hematite, rutile, kaolinite group minerals Hematite, rutile Hematite, rutile, goethite Hematite, rutile, goethite Hematite, rutile, kaolinite group minerals Hematite, rutile, kaolinite group minerals

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Major phases Diaspore, hematite Diaspore, hematite Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, hematite, kaolinite group minerals Diaspore, kaolinite group minerals Diaspore, kaolinite group minerals Diaspore Diaspore, kaolinite group minerals Diaspore, kaolinite group minerals Diaspore, kaolinite group minerals Diaspore Diaspore

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Samples R-1 R-2 R-3 R-4 R-5 R-6 R-7 R-8 R-9 R-10 R-11 R-12 R-13 R-14 R-15 R-16 R-17 R-18 R-19 R-20

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Journal Pre-proof Table 2- Results of the bulk chemical analyses of major oxides (wt.%) and trace and rare earth elements (ppm) for the bauxite ores, the basalts, and the dolomitic limestone of the Elika Formation in the Amir-Abad deposit. Samples No.

DL

SiO2 (wt.%) Al2O3 Fe2O3 CaO Na2O MgO K2O TiO2 MnO P2O5 LOI Sum U (ppm) Th Ba Hf Sr Ga Sc Co Nb Cs Rb V Y Ta Zr Ni Cr La (ppm) Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

0.01 0.01 0.04 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.1 0.2 1 0.1 0.5 0.5 1 0.2 0.1 0.1 0.1 8 0.1 0.1 0.1 20 10 0.1 0.1 0.02 0.3 0.05 0.02 0.05 0.01 0.05 0.02 0.03 0.01 0.05 0.01

R-1 BRO 32.01 29.35 24.15 0.21 0.11 0.11 0.31 3.09 0.43 0.22 9.92 99.91 7.6 21.8 222 14.5 288.2 21.9 30 277.4 112.5 7.9 110.0 599 59.2 6.8 343.6 408 715 245.3 473.2 40.65 120.1 15.11 2.45 11.92 1.88 9.98 1.83 4.84 0.66 4.14 0.62

R-2 BRO 32.01 28.89 23.81 0.25 0.12 0.12 0.29 3.14 0.48 0.23 10.58 99.92 6.6 21.1 178 13.6 233.2 20.5 30 289.4 110.4 7.7 87.9 583 68.7 5.7 323.8 358 684 124.4 443.1 29.31 117.1 29.32 6.65 15.31 2.09 12.01 2.31 6.35 0.86 5.62 0.86

R-3 BRO 25.98 34.25 23.01 0.21 0.09 0.11 0.23 4.14 0.42 0.22 11.23 99.89 9.5 23.3 141 14.5 182.3 21.6 34 274.1 130.2 4.6 69.8 674 41.5 9.7 406.2 383 702 136.2 280.1 33.12 121.4 21.74 5.78 14.82 2.29 13.17 2.31 6.82 0.99 6.62 0.95

R-4 BRO 22.59 39.65 22.14 0.16 0.09 0.07 0.22 4.85 0.31 0.15 9.70 99.93 14.1 27.5 150 16.3 196.3 24.8 39 260.5 165.3 4.8 74.3 761 38.8 9.3 448.3 336 668 177.1 231.2 34.25 111.1 15.02 3.75 9.92 1.67 9.72 1.82 5.03 0.73 5.11 0.72

R-5 BRO 21.12 29.98 22.14 0.21 0.11 0.11 0.26 3.19 0.43 0.22 12.13 89.90 7.8 20.2 192 12.3 251.2 18.6 31 235.4 116.5 5.7 94.6 615 47.6 6.1 336.1 331 668 119.3 284.2 29.71 106.5 15.72 3.84 12.32 2.03 11.54 2.43 6.82 0.98 6.14 0.93

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R-6 BRO 31.28 30.12 22.56 0.21 0.11 0.12 0.23 3.54 0.41 0.23 11.12 99.93 8.3 21.3 175 14.6 228.6 21.6 28 270.5 113.9 6.3 86.3 641 73.9 6.5 381.6 297 747 98.2 216.3 25.52 99.2 25.12 7.81 22.22 3.42 19.17 3.41 8.53 1.18 6.87 1.01

R-7 BRO 25.85 38.65 21.14 0.14 0.06 0.09 0.16 4.71 0.27 0.16 8.71 99.94 11.6 27.8 119 15.9 155.3 23.5 37 223.4 163.5 3.7 58.7 687 72.7 11.5 448.4 233 693 77.9 211.2 24.21 110.1 26.22 5.91 23.33 3.04 15.39 2.69 6.91 0.99 6.07 0.83

R-8 BRO 26.14 37.84 21.61 0.14 0.07 0.07 0.21 4.68 0.27 0.13 8.76 99.92 10.2 24.5 110 17.2 153.2 25.9 36 255.1 159.4 3.9 54.2 736 38.4 11.5 483.4 238 693 118.4 222.3 23.32 87.3 14.98 4.08 11.41 1.94 10.96 2.03 5.53 0.79 5.02 0.74

R-10 RO 21.54 42.99 20.84 0.09 0.06 0.06 0.16 4.54 0.17 0.11 9.39 99.95 15.5 28.3 98 18.3 128.3 27.1 43 240.5 171.3 3.3 33.7 743 28.6 9.7 497.2 316 678 99.4 195.8 21.21 75.2 16.72 3.92 16.44 3.05 17.62 3.19 8.97 1.28 7.74 1.04

R-11 RO 26.63 39.11 19.08 0.14 0.08 0.08 0.19 4.53 0.26 0.15 9.66 99.91 17.8 26.5 100 17.4 130.1 26.5 40 218.4 168.5 3.6 44.1 741 33.4 11.6 483.5 208 655 62.7 151.3 15.12 60.8 13.71 3.55 14.42 2.51 15.14 3.17 9.42 1.24 8.22 1.15

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R-9 BRO 22.01 41.87 21.02 0.09 0.06 0.06 0.12 5.04 0.19 0.11 9.36 99.93 13.7 26.8 83 16.6 108.6 24.8 40 225.3 165 1.5 40.9 732 50.3 12.8 476.8 252 644 89.2 241.1 18.81 70.1 13.52 3.98 12.81 2.12 12.12 2.28 6.38 0.88 5.52 0.73

R-12 RO 19.92 44.87 19.07 0.14 0.05 0.07 0.17 5.12 0.25 0.08 10.19 99.93 19.8 33.3 88 20.1 115.4 30.3 45 227.8 190.6 4.1 43.3 777 58.3 10.1 567.2 196 698 66.8 145.3 15.94 59.3 11.03 3.24 11.91 2.06 11.92 2.24 6.21 0.84 5.55 0.77

R-13 RO 22.14 44.88 18.06 0.13 0.04 0.06 0.08 4.78 0.25 0.12 9.41 99.95 22.7 29.3 78 20.5 92.3 30.2 42 213.2 170.3 1.3 38.5 764 71.9 12.8 525.2 156 650 38.9 145.2 9.22 36.2 8.02 2.44 8.42 1.53 9.53 1.98 5.87 0.81 5.02 0.75

R-14 RO 21.35 45.23 17.75 0.11 0.04 0.05 0.11 5.55 0.21 0.12 9.38 99.90 23.8 30.3 65 19.6 85.6 29.2 43 196.5 192.7 1.8 32.1 810 54.8 13.2 588.9 198 604 26.1 91.1 9.21 40.3 12.31 3.44 15.21 2.71 17.62 3.52 9.83 1.34 8.54 1.21

R-15 RO 13.69 50.88 18.06 0.04 0.03 0.02 0.13 5.69 0.08 0.05 11.23 99.90 30.7 36.5 56 19.6 82.6 29.9 48 201.4 209.6 3.5 27.6 834 38.6 12.4 642.3 161 612 32.7 75.1 11.11 52.3 15.98 2.94 16.78 2.54 14.42 2.84 7.47 1.01 6.33 0.99

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Journal Pre-proof Continued. Samples No. SiO2 (wt.%) Al2O3 Fe2O3 CaO Na2O MgO K2O TiO2 MnO P2O5 LOI Sum U (ppm) Th Ba Hf Sr Ga Sc Co Nb Cs Rb V Y Ta Zr Ni Cr La (ppm) Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

R-16 RO 25.21 40.45 17.55 0.11 0.07 0.06 0.21 4.96 0.23 0.14 10.93 99.92 21.3 29.8 168 18.7 210.1 28.6 41 201.4 170.3 4.4 83.8 743 103.0 10.8 521.6 155 611 41.8 124.9 7.97 29.8 6.82 1.74 5.88 0.98 5.78 1.06 2.98 0.41 2.81 0.42

R-17 RO 13.96 51.23 17.42 0.07 0.02 0.03 0.01 5.95 0.15 0.09 11.02 99.95 29.8 34.5 16 20.2 20.1 30.4 49 200.4 206.8 0.2 7.6 916 49.5 14.6 638.7 159 690 30.2 123.3 7.52 31.4 8.74 2.31 7.44 1.23 7.33 1.42 4.24 0.58 3.81 0.58

R-18 RO 14.89 50.99 16.59 0.07 0.04 0.03 0.08 5.74 0.15 0.06 11.31 99.95 31.9 35.8 26 20.9 53.6 31.6 51 199.3 210.7 1.5 12.6 874 105.0 13.5 621.9 179 663 28.7 83.6 7.78 35.8 9.01 2.13 10.52 1.83 11.53 2.24 6.42 0.91 5.91 0.85

R-19 RO 17.72 48.21 16.32 0.11 0.04 0.06 0.06 5.19 0.21 0.12 11.9 99.94 29.8 35.4 58 18.4 75.3 27.5 49 188.7 190.3 0.2 27.6 834 91.5 12.4 577.3 161 654 20.2 56.1 6.39 27.1 8.92 3.14 15.55 2.92 18.65 3.88 11.14 1.54 9.22 1.32

R-20 RO 15.23 51.24 14.65 0.08 0.03 0.05 0.11 5.95 0.17 0.09 12.36 99.96 30.4 36.9 85 22.1 111.2 33.9 52 164.2 211.3 2.5 42.1 887 64.4 13.5 644.5 118 642 20.4 74.5 5.12 21.5 5.21 1.63 5.37 1.04 6.33 1.32 3.65 0.51 3.52 0.45

B-1 Basalt 51.23 13.61 12.22 6.21 4.41 6.34 2.08 1.79 0.21 0.34 1.32 99.76 0.9 3.3 62 5.1 220.3 26.6 28 46.3 39.8 13.2 110.3 342 37.1 1.3 201.3 26 210 26.3 58.8 7.73 32.3 7.72 2.21 8.72 1.34 7.36 1.48 3.91 0.51 3.11 0.45

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B-2 Basalt 51.43 13.41 13.66 6.71 3.13 5.65 2.63 1.86 0.15 0.22 0.84 99.69 1.3 4.8 392 4.2 300.6 21.5 25 32.8 42.3 12.9 38.4 260 31.2 1.1 192.1 28 216 28.4 57.3 7.42 27.7 6.91 0.97 6.83 1.05 6.32 1.22 3.46 0.52 2.72 0.39

B-3 Basalt 50.82 13.47 12.33 7.75 4.33 5.88 2.35 1.81 0.19 0.15 0.88 99.96 0.4 1.6 96 3.2 240.1 20.5 24 38.7 36.9 17.7 55.6 235 23.7 0.7 189.6 41 232 13.7 30.2 4.24 17.6 4.78 1.35 5.11 0.75 5.05 0.92 2.41 0.35 2.13 0.28

B-4 Basalt 49.65 13.21 13.65 8.23 2.65 5.74 2.88 1.83 0.22 0.19 1.54 99.79 0.3 1.4 221 3.1 292.3 20.9 29 42.3 46.5 16.6 13.6 269 26.5 0.9 174.6 55 276 16.6 37.2 5.14 21.1 5.55 1.48 5.72 0.93 5.27 1.06 2.47 0.35 2.22 0.33

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DL-1 Dolomitic limestone 15.26 1.68 0.63 43.06 0.01 6.37 0.35 0.11 0.06 0.09 32.35 99.97 0.3 0.33 397 0.1 203.3 0.6 1 0.2 15.4 0.3 0.6 12 3.4 0.1 145.3 21 11 4.9 19.4 0.97 0.5 0.27 0.08 0.43 0.08 0.42 0.08 0.29 0.04 0.23 0.03

DL-2 Dolomitic limestone 16.65 2.14 0.46 42.44 0.01 5.42 0.31 0.15 0.04 0.18 32.14 99.94 0.3 0.31 306 0.2 196.4 0.5 1 0.3 10.1 0.1 0.2 8 4.1 0.1 125.8 20 12 1.9 8.4 0.35 0.6 0.17 0.06 0.37 0.08 0.59 0.12 0.39 0.04 0.25 0.03

DL-3 Dolomitic limestone 15.75 1.88 0.32 43.16 0.01 4.27 0.26 0.16 0.03 0.86 33.02 99.72 0.3 0.09 357 0.2 178.1 0.5 1 0.7 10.6 0.1 0.2 8 4.5 0.1 114.6 22 11 2.1 9.3 0.36 0.5 0.18 0.07 0.41 0.08 0.61 0.12 0.36 0.05 0.27 0.03

Abbreviations: DL= detection limit, LOI = loss on ignition, BRO = brownish red ore, RO = red ore. Samples of B-1 to B-4 are from the basalts within the carbonate of the Elika Formation. Samples of DL-1 to DL-3 are from the dolomitic limestone of the Elika Formation.

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Journal Pre-proof Table 3- Calculated parameters and elemental ratios, along with Eu and Ce anomalies for the bauxite ores, the basalts, and the dolomitic limestones of the Elika Formation in the Amir-Abad deposit. Sample No. Ti/Zr Nb/Ta Sm/Nd ΣLREE (La-Eu) (ppm) ΣHREE (Gd-Lu) (ppm) ΣREE (La-Lu) (ppm) (ΣLREE/ΣHREE)N (La/Yb)N La/Y Eu/Eu* Ce/Ce* CIA

R-1 BRO 53.91 16.54 0.13 896.81 35.87 932.68 14.20 40.03 4.14 0.54 1.03 97.03

R-2 BRO 58.14 19.37 0.25 749.88 45.41 795.29 9.38 14.96 1.81 0.93 1.69 96.77

R-3 BRO 61.10 13.42 0.18 598.34 47.97 646.31 7.08 13.90 3.28 0.96 0.97 97.78

R-4 BRO 64.86 17.77 0.14 572.42 34.72 607.14 9.36 23.42 4.56 0.91 0.67 98.32

R-5 BRO 56.90 19.10 0.15 559.27 43.19 602.46 7.36 13.13 2.51 0.82 1.11 97.26

R-6 BRO 55.62 17.52 0.25 472.15 65.81 537.96 4.08 9.66 1.33 0.98 1.01 97.38

R-7 BRO 62.97 14.22 0.24 455.54 59.25 514.79 4.37 8.67 1.07 0.71 1.15 98.66

Ti/Zr Nb/Ta Sm/Nd ΣLREE (La-Eu) (ppm) ΣHREE (Gd-Lu) (ppm) ΣREE (La-Lu) (ppm) (ΣLREE/ΣHREE)N (La/Yb)N La/Y Eu/Eu* Ce/Ce* CIA

R-16 RO 57.01 15.77 0.23 213.03 20.32 233.35 5.95 10.05 0.41 0.82 1.53 98.68

R-17 RO 55.85 14.16 0.28 203.47 26.63 230.10 4.34 5.36 0.61 0.85 1.90 99.67

R-18 RO 55.33 15.61 0.25 167.02 40.21 207.23 2.36 3.28 0.27 0.65 1.31 99.45

R-19 RO 53.90 15.35 0.33 121.85 64.22 186.07 1.08 1.48 0.22 0.79 1.17 99.32

R-20 RO 55.35 15.65 0.24 128.36 22.19 150.55 3.29 3.92 0.32 0.91 1.69 99.39

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B-1 Basalt 53.31 30.62 0.24 135.06 26.88 161.94 2.85 5.71 0.71 0.80 0.97 39.56

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B-2 Basalt 58.05 38.45 0.25 128.70 22.51 151.21 3.25 7.05 0.91 0.42 0.92 39.90

B-3 Basalt 57.23 52.71 0.27 71.87 17.00 88.87 2.40 4.35 0.58 0.81 0.93 36.18

R-9 BRO 63.37 12.89 0.19 436.71 42.84 479.55 5.79 10.92 1.77 0.90 1.34 99.07

R-10 RO 54.74 17.66 0.22 412.25 59.33 471.58 3.95 8.68 3.48 0.70 0.97 99.00

B-4 Basalt 62.84 51.67 0.26 87.07 18.35 105.42 2.70 5.05 0.63 0.78 0.95 37.05

R-11 RO 56.17 14.53 0.23 307.18 55.27 362.45 3.16 5.15 1.88 0.75 1.14 98.51

R-12 RO 54.12 18.87 0.19 301.61 41.50 343.11 4.13 8.13 1.15 0.84 1.03 98.85

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R-8 BRO 58.04 13.86 0.17 470.38 38.42 508.80 6.95 15.94 3.08 0.93 0.95 98.45

DL-1 Dolomitic limestone 4.54 154.00 0.54 26.12 1.60 27.72 9.27 14.39 1.44 0.70 2.00 2.09

R-13 RO 54.56 13.30 0.22 239.98 33.91 273.89 4.02 5.24 0.54 0.88 1.77 99.14

DL-2 Dolomitic limestone 7.15 101.00 0.28 11.48 1.87 13.35 3.49 5.14 0.46 0.71 2.29 2.69

R-14 RO 56.50 14.60 0.31 182.46 59.98 242.44 1.73 2.07 0.48 0.75 1.39 99.16

R-15 RO 53.11 16.90 0.31 190.13 52.38 242.51 2.06 3.49 0.85 0.53 0.93 99.49

DL-3 Dolomitic limestone 8.37 106.00 0.36 12.51 1.93 14.44 3.68 5.26 0.47 0.76 2.35 2.33

(ΣLREE/ΣHREE)N = (ΣLREE/ΣHREE) bauxite ore/(ΣLREE/ΣHREE) chondrite, (La/Yb)N = (La/Yb) bauxite ore/(La/Yb) chondrite, Eu/Eu* = EuN/√(SmN*GdN), and Ce/Ce* = (2CeN)/(LaN+PrN) (N = normalized to values of chondrite). CIA = [molar Al2O3/(molar Al2O3 + CaO* + Na2O + K2O)] × 100. CaO* is the amount of CaO incorporated in silicate fraction of the samples measured. Abbreviations same as Table 2. Values of chondrite are from Taylor and McLennan (1985).

Table 4- Some geochemical characteristics (e.g., CIA, Eu/Eu*, Ce/Ce*, La/Y, (La/Yb)N, (ΣLREE/ΣHREE)N, origin, and parent rock) of the Amir-Abad bauxite deposit compared with those of some well-known bauxite deposits in the world. Note that N represents normalized to values of chondrite of Taylor and McLennan (1985). CIA

Eu/Eu*

Ce/Ce*

La/Y

(La/Yb)N

(ΣLREE/ΣHREE)N

Origin

Parent rock

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Journal Pre-proof South CameroonA Apulian bauxites (southern Italy)B Jamnagar (India)C Balkouin (Burkina Faso)D Lower Cretaceous (NE Spain)E Fusui area (Guangxi Province, South China)F Zagrad (Montenegro)G Xiaoshanba (Central Guizhou Province, China)H Northern Guizhou Province (China)I Yunfeng (Guizhou, China)J Darzi-Vali (NW Iran) Arbanos (NW Iran)L

K

Bidgol (ZSFB, Iran)M N

Semirom (ZSFB, Iran) Parnassos–Ghiona (Greece)O Amir-Abad (NW Iran)P Abbreviations same as Table 3. A Beyala et al. (2009). B Mongelli et al. (2014). C Meshram and Randive (2011). D Giorgis et al. (2014). E Yuste et al. (2017). F Yu et al. (2014). G Radusinović et al. (2017). H Ling et al (2018). I Gu et al. (2013). J Long et al. (2017). K Khosravi et al. (2017). L Abedini et al. (2019). M Ahmadnejad et al. (2017). N Ellahi et al. (2019). O Gamaletsos et al. (2019). P This study.

51.8–97.8 96.7–99.3 64.3–94.7 48.2–99.4 96.3–99.9 97.7–100.0 90.4–99.9 78.1–99.8 81.5–98.9

0.6–0.7 0.7–0.9 0.7–1.1 0.8–1.2 0.58–0.64 0.4–0.6 0.6–0.7 0.5–0.7 0.5–1.0

0.9–1.4 0.3–3.3 0.5–1.0 0.7–1.1 0.6–2.1 0.3–10.9 0.1–2.9 0.9–1.3 0.8–3.9

1.1–3.6 0.2–5.2 1.8–5.4 0.2–2.0 0.5–5.8 1.1–1.5 0.2–7.3 0.04–4.2

4.1–8.6 4.7–14.5 2.6–32.6 12.0–28.1 0.9–18.6 2.1–25.1 2.9–8.5 1.8–33.2 0.3–17.2

2.4–6.4 3.1–11.2 1.6–10.7 5.8–11.7 0.9–7.2 1.5–20.1 6.0–58.1 0.9–18.1 0.4-12.0

-

0.6–0.8

0.7–1.4

0.2–4.7

1.5–22.8

1.1–12.1

92.8–99.0 89.3–98.8

0.8–0.9 0.8–1.0

0.8–2.5 0.8–1.3

0.7–5.8 0.3–12.3

10.1–68.6 4.0–68.6

12.5–13.2 2.3–10.4

26.2–99.6

0.5–0.7

0.5–1.8

0.4–3.6

5.2–46.1

96.8–99.7

0.2–2.9 0.6–0.7 0.5–1.0

0.7–2.4 0.7–7.6 0.7–1.9

0.5–9.7 0.2–1.9 0.2–4.6

2.8–58.6 1.4–12.5 1.5–40.0

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2.0–19.9 1.9–11.0 1.1–14.2

Autochthonous Autochthonous Autochthonous Autochthonous Autochthonous to allochthonous Autochthonous Autochthonous Autochthonous to allochthonous Autochthonous Allochthonous Allochthonous

Distal magmatic materials and continental clastic Trachyte/andesite Intrusive rock Mafic argillaceous sediments Clastic materials and volcanic source Underlying dolomite Shale and limestone derived from basic rocks Dolomite and black rock sequence Basalt Shale Argillaceous limestone Clayey component within the underlying limestone Basalt

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Journal Pre-proof Conflict of interest

This paper has not conflict of interest

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Journal Pre-proof Graphical abstract

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Journal Pre-proof Highlights - We determine the behavior of elements during weathering processes and mass change calculations. - The bauxite ores with La/Y< 1 have higher CIA values than the bauxite ores with La/Y> 1. - Mineral control and physico-chemical conditions had effective roles in the behavior of elements. - Basalt was a plausible source rock for the bauxite ores.

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