Mineralogical, Geochemical and Isotopic Investigation of the Akdağ (D ivriği -Sivas) Iron Deposit, Turkey Ece Varol 1, Taner Ünlü 1 1 Ankara University

Mineralogical, Geochemical and Isotopic Investigation of the Akdağ (Divriği-Sivas) Iron Deposit, Turkey

Ece Varol1, Taner Ünlü1 1Ankara University

Most of the Turkish iron ore production comes from central-eastern Anatolia, and the iron deposits in the Sivas–Malatya region account for about 61% of the country’s production. The Akdag deposit, located in the vicinity of Divrigi region in southeastern Sivas, Turkey, is a chemical sedimentary type iron deposit. Iron deposit was formed concordantly to the bedding within the Bozbel Formation which is composed of sandstone with ore pebbles and Nummulitic limestone-marl alternation.

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In this study, depositional environment of the Akdag iron deposit is discussed in regard to mineralogical, geochemical and isotopic data. In the Akdag iron deposit, magnetite is the primary ore mineral, whereas goethite and hematite are secondary ones. XRD patterns and ore microscopy studies indicate that sedimentation also played an important role in deposition.

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During the deposition process, iron was transported to the marine environment where it was deposited in aqueous and also fragmental form. Stable isotope data (δ18O) on hematite samples yield that the ore is not associated with the hydrothermal fluids and δ18O values resemble those of the banded iron formations (BIF) indicating a sedimentary precipitation.

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As a result of studies, Akdag iron mineralization is of chemical sedimentary type and was deposited in a shallow marine environment (hdyrogenetic). Iron is most likely transported to this environment in detritic, adsorbsive, absorbtive, colloidal or/and gel state from the older iron deposit or underlying ultramafic rocks. Karstification developed within fault zones remobilized the ore. By this way, the iron deposit took its present shape and character.

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Iron deposit was formed concordantly to the bedding within the Bozbel Formation which is composed of sandstone with ore pebbles and Nummulitic limestone-marl alternation. As a result of post-depositional processes, the mineralization was tectonically emplaced within the host rocks. Based on fossil assemblage, the deposit is of Cuisian age.There are debates about the occurrence of the deposit and according to some researchers (Öztürk 2005) primary ore which is developed in limestone with intrusion by hydrothermal fluids was formed along a serpentinite-limestone through karstic processes. There are also other studies stating that the ore deposit is either tectonically situated within the limestone and demonstrates sedimentary (conglomeratic) bedding properties (Ünlü and Stendal 1986, 1989). Moreover, this deposit is interpreted to have been deposited in a shallow marine environment (Yılmaz et al., 2005).



In the Akdag iron deposit, magnetite is the primary, hematite and goethite are secondary ore minerals.

In ore microscopy, two types of hematite and goethite are discriminated:

The first type hematite is transformed from euhedral magnetite which partly shows sign of transportation and has been martitized along the relicts.

The second type hematite occurs replacing the sedimentary grains revealed by typical ringförmig and colloidal structures.

The first type goethite is formed by alteration of hematite.The second type goethite settles down in a later stage and

fill the space between magnetite grains.

Pinkish-gray magnetite stains and relict textures in completely hematized magnetites; white parts are martite (sample No: 19)

Hematited magnetite and goethite mineral dissolution in edge-crack (sample No: 46)

Hematite layers (Sample No: 46)

Ore Microscopy and SEM images



Layer surface

Kalsitin boşalttığı hacimce yerleşen hematitler, küresel oluşumlar (Örnek No:42)

a) Hematite forming a "ringförmig" structure, b) Goethite substituting hematite, cement grains and gangue (Sample No: 14)

a) Hematite replaces carbonate gangue (at the right side approx.75°-angle romboeder shapes) and gangue is substituted by hematite b) The hematite is substituted along a crack by a young gangue (Sample No:42)



Spherical hematite

1st Group 2nd Group

In the first group ores, calcite and dolomite contents are higher but iron minerals are in relatively low abundance.



In the second group ores, calcite and dolomite contents are low but iron minerals are dominated.

XRD Patterns



REE’s of ore samples are found to be enriched 10- to 100-fold with respect to PAAS and NASC. In comparison with chondrite, LREE’s are enriched 1 to 50-fold whilst HREE’s remained unchanged. This indicates that ore composition is close to marine characteristics. Weak Ce and Eu negative anomalies are hardly visible in the same graph.

Trace element geochemistry

(Wonder et al., 1988)

(Nicholson, 1992)

(Hren et al., 2006)



Detritic iron derived from weathering of terrestrial units may be transported to the marine environment. Relations between major, trace and rare earth elements indicate that in the course of deposition of Akdağ iron ore, iron (detrital) was dissolved in the seawater and partly preserved its primary ore form. Such ores deposits within the aqueous environment called “hydrogeneous” type.



Fe2O3 values of ore samples are divided into two groups. Values of the first group are between 70-93 %, whereas those of second group range from 90 to 94 %.

In the studied iron deposit, Eu/Eu*, (La/Yb)n and Ce/Ce* ratios are 1.63 (average), 1 and 0.75-1.06, respectively. The average HREE and LREE values are 0.15 and 1.25. La/Ce and Y/Ho ratios are 0.5-1 and 10-36.

Low La/Ce and high Y/Ho ratios and HREE enriched patterns encourage that the Akdag iron deposit was precipitated in a shallow marine environment.



According to stable isotope studies conducted on calcite and dolomite samples of the carbonate host rocks, δ13C values (VPDB) are -5.91 to +3.52 permil for calcites and -1.01 to +5.68 permil for dolomites and δ18O values (VSMOW) are +21.94 to +27.27 permil for calcites and +25.39 to +29.55 permil for dolomites.

δ18O and δ13C Isotope composition of calcite and dolomite (carbonate host rocks)

In dolomite samples increasing MgO and CaO concentrations with enrichment of heavy oxygen (18O) and carbon (13C) isotopes of the carbonate host rocks is explained by evaporation and/or diagenesis. It is determined that Sr concentration of dolomites is reduced as the δ18O and δ13C values are lowered. It can be said that dolomites in study area most are likely interacted with fluids which have different Sr concentrations. Without Sr isotope data, it is hard to speculate that fluids are of metamorphic or magmatic origin.



δ18O values of hematite samples are between -2.49 and -0.01 ‰.



δ18O Isotope composition of hematite

HematiteMagnetite

HematiteMagnetite

HematiteMagnetite



In diagrams where δ18O values are plotted against SiO2, MgO and Fe2O3, a positive correlation between concentrations of these elements and heavy oxygen isotope (18O) in hematite samples might indicate a magmatic and/or metamorphic source.

In δ18O values plotted against SiO2, MgO and Fe2O3 diagrams, hematite and magnetite samples fall into different areas because magnetite has I-18O index grater than that of hematite.

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Mineralogical, Geochemical and Isotopic Investigation of the Akdağ (D ivriği -Sivas) Iron Deposit, Turkey Ece Varol 1, Taner Ünlü 1 1 Ankara University