Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye)

Yılmazer, Erkan; Terzi, Mustafa Haydar

doi:10.3390/min15050528

Open AccessArticle

Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye)

by

Erkan Yılmazer

^*

and

Mustafa Haydar Terzi

Department of Geological Engineering, Aksaray University, Aksaray 68100, Türkiye

^*

Author to whom correspondence should be addressed.

Minerals 2025, 15(5), 528; https://doi.org/10.3390/min15050528

Submission received: 10 April 2025 / Revised: 9 May 2025 / Accepted: 13 May 2025 / Published: 15 May 2025

(This article belongs to the Section Mineral Deposits)

Download

Browse Figures

Versions Notes

Abstract

:

The Kesikköprü iron deposit, located in the Central Anatolian Crystalline Complex, occurs in the triple contact of Kesikköprü granitoid, mafic–ultramafic rocks, and marble. The causative Kesikköprü granitoid, consisting of diorite, granodiorite, and granite, is classified as sub-alkaline, calc-alkaline, and shoshonitic, displaying metaluminous to partially peraluminous properties. Sr-Nd isotope data and the geochemical characteristics of the Kesikköprü granitoid indicate a metasomatized mantle origin, with its ultimate composition arising from crustal contamination and magma mixing along with fractional crystallization in a post-collisional setting. The ⁴⁰Ar/³⁹Ar geochronology reveals a total fusion age of 73.41 ± 0.32 Ma for the biotite of the Kesikköprü granitoid. The alteration pattern in the deposit is characterized by an endoskarn zone comprising garnet–pyroxene (±phlogopite ± epidote) and an exoskarn zone displaying a zoning of garnet (±pyroxene ± phlogopite), pyroxene (±garnet ± phlogopite ± epidote), epidote–garnet, and epidote-rich subzones. Magnetite is extracted from massive lenses within the exoskarn zones and shows vein, disseminated, banded, massive, and brecciated textures. The low potassium content of phlogopites which are associated with magnetite mineralization prevents the determination of a reliable alteration age. δ¹⁸O thermometry reveals a temperature range between 462 and 528 °C for the magnetite mineralization. According to geochemical (trace and rare earth elements), stable (δ¹⁸O, δ²H, δ³⁴S, and δ¹³C), and radiogenic (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) isotope data, the hydrothermal fluid responsible for the alteration and mineralization is related to the Kesikköprü granitoid, from which a significant magmatic component originates initially, followed by meteoric fluids at lower temperatures (123 °C) during the late-stage formation of calcite–quartz veins.

Keywords:

Ar-Ar; Kesikköprü granitoid; stable isotopes; magnetite; skarn

1. Introduction

Iron ore is a critical raw material for the iron and steel industry, playing an essential role in the economic development of industrialized countries. Consequently, global iron demand has been steadily increasing, with iron ore production rising from 1.87 billion metric tons (Gt) in 2010 to approximately 2.5 Gt in 2023, excluding a production decline mainly due to the impacts of the COVID-19 pandemic in 2020 [1,2]. Türkiye has approximately 900 iron ore prospects and/or deposits, yet only about 30 of them are currently being exploited, contributing to the country’s overall iron ore resource of approximately 2500 million metric tons [3,4,5]. Iron ore production in Türkiye, similar to the global trend, reached 6.5 Mt in 2011, 21.5 Mt in 2020, and 16.8 Mt in 2023 [6]. Most iron deposits are geographically located in central and central-eastern Anatolia—especially in the Sivas-Malatya, Kayseri-Adana, and Ankara-Kırşehir regions—as well as in western Anatolia (Biga peninsula) (Figure 1a) [7]. The primary iron deposits in central and central-eastern Anatolia are linked to the Central Anatolian Crystalline Complex (CACC), one of the six major continental terranes in Türkiye (Figure 1b,c) [8,9]. The CACC hosts several mineral deposits, including metasedimentary (Fe and Ba), skarn (Fe, W, and Pb-Zn), vein-type (Mo-Cu, Sb-Hg-W, and fluorite), orogenic gold, and sedimentary–volcanic deposits (diatomite, kaolinite, bentonite, uranium, sulfur, salt, perlite, and pumice) [10,11,12]. Among these, Fe-skarns are the most prominent group within its metallogeny. These deposits occur in the binary or triple contacts between the Central Anatolian Granitoids (CAGs), the Central Anatolian Metamorphics (CAMs), and/or the Central Anatolian Ophiolites (CAOs) (Figure 1c) [11,13]. Almost all are calcic exoskarn and are classified as Fe, W, and Pb-Zn skarns based on their dominant metal content [10,11]. The general characteristics of some Fe-skarn deposits in the central and central-eastern Anatolian are presented in Table 1.

The Kesikköprü iron deposit, approximately 110 km southeast of Ankara, is located within the Fe-skarn metallogenic belt of Kuşcu and Erler [11], which extends from Sivas through Akdağmadeni (Yozgat) and to Kesikköprü (Ankara). Mineralization occurs at the triple contact between marble of the CAM; gabbro and pyroxenite of the CAO; and granite, granodiorite, and monzonite of the CAG. The Kesikköprü iron deposit is one of the best-exposed iron skarns among the iron districts in the central and central-eastern Anatolia (Figure 1). The iron ore is produced from magnetite-rich lenses in the exoskarn zones with a total resource of 12.7 Mt at 39 to 61% Fe [5]. Mining operations date back to the 1960s and magnetite is still being extracted from an open pit with an iron production capacity of 0.3 Mt/year in the partnership with Özce and Güncem Mining Companies [14]. The produced ore is transported to the Yahşihan (Kırıkkale) train station and then by railway to the Karabük Iron and Steel factories [15].

Figure 1. (a) Distribution of the iron prospects or deposits in Türkiye [3,5,16] (iron–producing districts: (1) Aydın–İzmir; (2) Biga; (3) Kütahya; (4) Sakarya–Çamdağ; (5) Ankara–Kırşehir; (6) İçel; (7) Kayseri–Adana; (8) Payas–Kilis; (9) Sivas–Malatya; (10) Giresun). (b) Tectonic map of the major continental terranes in Türkiye and the location of CACC [9]. (c) Simplified geological map showing the distributions of major rock units in the CACC [9,17,18] (AKM: Akdağmadeni Massif; CACC: Central Anatolian Crystalline Complex; CP: Central Pontide; DSF: Dead Sea Fault; EFZ: Ecemiş Fault Zone; EP: Eastern Pontide; IAESZ: İzmir–Ankara–Erzincan Suture Zone; IPS: Intra-Pontide Suture; ITS: Inner-Tauride Suture; IZ: Istanbul Zone; KM: Kırşehir Massif; MM: Menderes Massif; NM: Niğde Massif; RSZ: Rhodope–Strandja Zone; SZ: Sakarya Zone; TB: Thrace Basin; TGFZ: Tuz Gölü Fault Zone).

Table 1. The characteristics and common features of some iron deposits in the central and central-eastern Anatolian.

Deposit Name (Location)	Kesikköprü (Ankara)	Çelebi (Kırıkkale)	Karamadazı (Kayseri)	Divriği (Sivas)			Hekimhan (Malatya)
Deposit Name (Location)	Kesikköprü (Ankara)	Çelebi (Kırıkkale)	Karamadazı (Kayseri)	A Kafa	B Kafa	Dumluca	Hasançelebi
Commodity	Fe	Fe, W	Fe	Fe	Fe, Cu	Fe	Fe, Cu, Au
Host Rock	(1) Marble	(1) Marble	(1) Limestone	(1) Limestone	(1) Limestone	(1) Limestone	(1) Volcanics
	(2) Mafic–ultramafic	(2) Granitoid	(2) Granitoid	(2) Serpantinized ultramafic	(2) Serpantinized ultramafic	(2) Serpantinized ultramafic	(2) Siyenite
	(3) Granitoid	-	-	(3) Monzonite and monzodiorite	-	(3) Siyenite, granite, and diorite	-
Age of Host Rock (Method)	(1) Paleozoic–Mesozoic	(1) Paleozoic–Mesozoic	(1) Permian	(1) Mesozoic	(1) Mesozoic	(1) Mesozoic	(1) 74.26 ± 0.45 to 76.84 ± 0.67 Ma (Ar-Ar)
	(2) Late Cretaceous	(2) 72.9 ± 1.2 to 74.24 ± 0.66 Ma (Ar-Ar)	(2) 48.74 ± 0.67 Ma (Ar-Ar)	(2) Late Cretaceous	(2) Late Cretaceous	(2) Late Cretaceous	(2) 71.27 ± 0.29 to 75.07 ± 0.5 Ma (Ar-Ar, K-Ar, and U-Pb)
	(3) 72.14 ± 0.81 to 73.41 ± 0.32 Ma (Ar-Ar)	-	-	(3) 62.1 ± 0.3 to 77.4 ± 1.5 Ma (Ar-Ar, K-Ar), 110 ± 5 Ma (Rb-Sr)	-	(3) 67.8 ± 0.4 to 76.6 ± 1.6 Ma (K-Ar)	-
Alteration Assemblages	Grt, Px, Ep, Cal, Qz, Phl, Ttn, and Tr	Grt, Px, Ep, and Qz	Grt, Px, Ep, Act, Qz, and Cal	Grt, Px, Ep, Amp, Scp, Ab, Phl, Ba, and Kfs	Se, Qz, Cal, and Ba	Phl, Grt, Px, Cal, and Qz	Scp, Phl, Act, Grt, Px, Se, Qz, Fl, and Ab
Ore Body Form	Massive, bands, and lenses	Dissemination, massive, and pockets	Pockets, dissemination, and lenses	Pockets, lenses, and massive	Brecciated	Massive	Dissemination, massive, and brecciated
Ore Minerals	Mag, Hem, Lim, Py, Ccp, Mrc, and Mlc	Mag, Sch, Spc, Hem, Py, and Ccp	Mag, Hem, Py, Ccp, and Mlc	Mag, Py, and Ccp	Hem, Gth, Lim, Py, Ccp, Mlc, and Mrc	Mag, Py, and Hem	Mag, Hem, Gth, Py, and Ccp
Reserve and Grade	12.7 Mt at 39%–61% Fe	0.961 Mt at 35%–42% Fe	6.4 Mt at 54% Fe	65.4 Mt at 45%–61% Fe		5.6 Mt at 57% Fe	865 Mt at 15% Fe;
		0.075 Mt at					0.04–2 ppm Au
		0.41% W					0.04%–2.75% Cu
Mineralization Age (Method)	-	-	46.58 ± 0.82 Ma (Ar/Ar)	73.5 ± 0.40 to 74.34 ± 0.83 Ma (Ar-Ar)	-	-	68.64 ± 0.42 to 74.92 ± 0.39 Ma (Ar-Ar)
References	[5,8,19,20,21,22,23,24], This study	[5,8,24,25]	[5,24,26]	[5,26,27,28,29,30,31]		[3,5,29,31]	[5,26,30,32]

Abbreviations: Act—Actinolite; Ab—Albite; Amp—amphibole; Ba—Barite; Cal—calcite; Ccp—chalcopyrite; Ep—epidote; Kfs—K-feldspar; Fl—Flourite; Grt—garnet; Gth—goethite; Hem—hematite; Lim—limonite; Mlc—malachite; Mag—magnetite; Mrc—marcasite; Pent—Pentlandite; Phl—phlogopite; Py—pyrite; Px—pyroxene; Scp—Scapolite; Sch—Scheelite; Se—sericite; Spc—Specularite; Ttn—titanite; Tr—tremolite; Qz—quartz.

Most studies on the Kesikköprü iron deposit have been conducted by the General Directorate of Mineral Exploration and Research (MTA). These studies cover the general geology of the region, the geological–economic status of the mineralization, the feasibility and resource development, and the identification of new resources in the region [33,34,35,36,37,38,39,40,41,42]. Some studies have focused on the mineralogy, petrography, and petrogenesis of the skarn formation and iron mineralization in the region [20,22,43], with a few investigating the origin of the iron mineralization [23]. Bayhan [20,22] reported that the skarns in the region were formed at temperatures ranging from 460 to 675 °C under pressures of 1.5 to 2 kbar, and exhibited zoning pattern consisting of garnet, garnet + clinopyroxene, and epidote from the granitoid to the marble. Doğan et al. [23] proposed that iron enrichment resulted from the serpentinization of ultramafic rocks and that granite intrusion led to the re-mobilization of iron toward the skarn zones.

Despite these studies on the Kesikköprü iron deposit, a significant gap remains in the understanding of the alteration–mineralization pattern, the physicochemical properties of the hydrothermal fluid (including its origin and temperature), and the geochemical processes and isotopic signatures on skarn formation, mineralization, and the associated granitoid. The age of the mineralization and host rock is still lacking, hindering the genesis and a comprehensive temporal and spatial framework of the mineralization and metallogeny of the region.

In this study, we aim to identify and classify the iron oxide-type mineralization and host rocks in the Kesikköprü region through a combination of geological, mineralogical–petrographical, and geochemical analyses. Our approach includes detailed mapping and sampling; geochemical studies focusing on major, minor, and rare earth elements; and radiogenic (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) and stable isotope analyses (δ¹⁸O, δ²H, δ¹³C, and δ³⁴S). Additionally, geochronological studies (Ar-Ar) have been conducted to determine the timing of the granitoid and mineralization. This integrated approach allows us, for the first time, to understand the mineral paragenesis, the temperature conditions of alteration–mineralization, the origin of the hydrothermal fluid, and the connections between the mineralization and the granitoid. We anticipate that a better understanding and modeling of the magmatic–hydrothermal system in this region will guide future research on existing iron mineralization and help assess the potential for other types of mineralization associated with the Kesikköprü granitoid. It will also provide an opportunity to compare these findings with other mineralizations in the region (such as Çelebi, Divriği, and Hekimhan) as well as with global systems.

2. Geological Framework

2.1. Regional Geologic Setting

The study area lies in the CACC, one of the distinct continental terranes in the Alpine–Himalayan orogenic system (Figure 1b,c) [9,17,44,45]. The CACC constitutes a significant component of the Anatolide–Tauride Platform that took its final configuration with the closure of the Neo-Tethys Ocean [17,45,46]. The CACC contains three metamorphic massifs: Kırşehir in the northwest, Akdağmadeni in the northeast, and Niğde in the south. It is flanked by the Ecemiş Fault Zone to the east, the Tuz Gölü Fault Zone to the west, and the İzmir–Ankara–Erzincan suture zone to the north (Figure 1c) [47].

The CACC comprises four main rock groups: (1) metamorphic rocks (CAMs), (2) ophiolitic rocks (CAOs), (3) granitoids (CAGs), and (4) cover units. The CAM, from old to young, consists of Kalkanlıdağ (equivalent to Gümüşler in the Niğde massif), Tamadağ (equivalent to Kaleboynu in the Niğde massif), and Bozçaldağ (equivalent to Aşıgedigi in the Niğde massif) formations [13,19]. The Kalkanlıdağ formation is characterized by a mixture of migmatite, gneiss, biotite schist, pyroxene schist, amphibole schist, quartzite, quartz schist, and calc-silicate schist, whereas the Tamadağ formation exhibits an alternating sequence of marble, schist, and gneiss, and the Bozçaldağ formation is predominantly composed of marble alternating with metachert layers [13,19]. The principal metamorphic event in the CACC occurred under medium pressure–medium-/high-temperature conditions transitioning to medium-/low pressure-high temperature conditions [13]. The timing of the metamorphism is recorded as 69.0 ± 1.7 (K-Ar: biotite) to 84.1 ± 0.8 Ma (U-Pb: monazite) in the Kırşehir massif [48,49,50], 68.11 ± 1.8 (K-Ar: biotite) to 77.71 ± 1.8 Ma (K-Ar: muscovite) in the Akdağmadeni massif [51], and 66.26 ± 0.36 (Ar-Ar: biotite) to 91 ± 0.2 (U-Pb: monazite) Ma in the Niğde massif [49,52,53].

The CAM is tectonically overlain by Late Cretaceous (Turonian–Santonian) by supra-subduction type ophiolitic mélange (CAO) [54]. This mélange, associated with the Neo-Tethys Ocean, consists of ultramafics, unlayered gabbro, plagiogranite, diabase, pillow lavas, and epi-ophiolitic sediments [13,54]. Unlike the upper levels, the bottom of the ophiolites in the CAO exhibits low-grade metamorphism and deformation structures, which occur simultaneously with the metamorphism of the CAM [13,55].

The granitoids (CAGs) in the CACC are categorized into several genetic associations, such as the two-mica granitic association (S-type), the high-K calc-alkaline I-S (hybrid, H)-type monzonitic association, and the alkaline syenitic association (A-type). The CAG cuts the CAM and CAO rock groups [8,10,11,21,47,54,56,57]. The post-collisional alkaline rocks of the region (A-type), called the central-eastern Anatolian alkaline syenitoids (CEASs) by Yılmaz and Boztuğ [56], cut the felsic to intermediate plutonic rocks (S- and H-types) of the CAG. The CEAS is also subdivided into two subgroups: silica-oversaturated alkaline (ALKOS) plutons and silica-undersaturated alkaline (ALKUS) plutons, with the latter being younger than the ALKOS plutons [57]. In accordance with the Streckeisen-QAP classification, the H-type rock unit of the CAG ranges from alkaline feldspar granite to tonalite for quartz content over 20%, from quartz monzonite to quartz diorite for quartz between 5 and 20%, and from monzonite to diorite for quartz below 5% [58]. According to their field characteristics, the S- and H-type granitoids are grouped as (1) two-mica leucogranites; (2) biotite/hornblende granites; (3) K-feldspar megacryst-bearing granites; (4) granodiorites; (5) tonalites; and (6) aplitic K-feldspar granites [58,59,60]. These granitoids are also geographically grouped into western, northern, and eastern groups [47,59]. The age (AFT, Ar-Ar, K-Ar, Pb-Pb, Rb-Sr, U-Pb, and total lead techniques) of the granitoids range between 54 and 110 Ma for the western group, 48 and 82 Ma for the northern group, and 42 and 110 Ma for the eastern group [8,24,26,27,29,49,52,53,54,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77]. This complex is unconformably overlain by the latest Maastrichtian–Paleocene and/or Eocene volcanoclastics and carbonates, Oligocene–Miocene evaporites and clastics, and Miocene–Plio-Quaternary continental clastic rocks [10,13,47,58,60,78,79,80].

2.2. Local Geology

The main rock units, exposed in the Kesikköprü region, are Paleozoic–Mesozoic marble in the CAM, Late Cretaceous mafic–ultramafic rocks in the CAO, Late Cretaceous-Paleocene granitoid in the CAG, and cover units (Figure 2a) [19,76,80].

Metamorphic rocks, the basement in the Kesikköprü region, mainly comprise marble with gneiss and schist intercalations [20]. Gneiss and schist notably contain cordierite, sillimanite, clinopyroxene, biotite, K-feldspar, plagioclase, quartz, muscovite, and sericite, bracketing the conditions of metamorphism at medium to high-temperature [20]. They are not present in the open pit area, whereas marble is exposed as irregularly distributed blocks within the mafic–ultramafic rocks (Figure 2b,c). The origin of the marble blocks is debatable as such some studies argued that they are olistolithic limestone blocks similar to Permian or Jurassic blocks commonly present within the ophiolitic rocks (CAOs), not to the Paleozoic–Mesozoic Bozçaldağ metamorphics of the CAM [23,39,81]. The precise definition of these marble blocks in the open pit area remains unclear due to the lack of fossil content, highly deformed structural (e.g., fractures and cracks), and textural (recrystallization) characteristics. The marbles are mostly grayish to white calcic to dark gray dolomitic in composition (Figure 3a). The fractures, cracks, and foliation planes of marbles are filled with secondary minerals, including calcite, chalcedonic quartz, magnetite, and sulfides (Figure 3b,c). The primary minerals in the marble are medium- to coarse-grained anhedral calcite, with a lesser extent of dolomite and ankerite. The grain size of marble increases toward the granitoid rocks [20,76,82,83].

The mafic–ultramafic rocks are widely exposed in the open pit area and are composed of pyroxenite, hornblendite, and gabbro. Gabbro displays cumulate texture [20] and contains a mineral assemblage comprising plagioclase, clinopyroxene, orthopyroxene, and hornblende (Figure 3d). The uralitized, chloritized, and epidotized clinopyroxene, along with secondary calcite and quartz, are commonly observed as alteration products in these rocks (Figure 3d,e).

The intrusive rocks in the region were initially named the Çelebi granitoid by Bayhan [21] and later referred to as the Kesikköprü granitoid by Doğan et al. [23] due to their widespread outcrops around the Kesikköprü region. The Çelebi granitoid is a composite plutonic body consisting of two distinct types. The first type (leucocratic) has a granitic composition, is more evolved, and appears light in color. The second type (mesocratic) ranges from dioritic to granodioritic, is more primitive, and is intermediate to dark in color [21,82,84]. According to Kuşcu et al. [82], Fe and W mineralization is associated with mesocratic and leucocratic rocks of the Çelebi granitoid, respectively. In this study, the southern section of the Çelebi granitoid, which covers an area of approximately 300 km², is referred to as the Kesikköprü granitoid, while the rest remains the Çelebi granitoid (Figure 1c). The Kesikköprü granitoid intrudes marble and the mafic–ultramafic rocks (Figure 3f) in the deposit site. It exhibits medium- to coarse-grained, holocrystalline–granular or holocrystalline–porphyritic textures and is granite, granodiorite, and monzonite in composition [20]. The granitoid consists of plagioclase, orthoclase, quartz, hornblende, biotite, clinopyroxene, titanite, and apatite minerals in varying proportions (Figure 3g), and is cut by numerous aplite dykes. The Kesikköprü granitoid contains rounded unreplaced mafic–ultramafic rock fragments (Figure 3h), as well as enclaves in monzonite, monzodiorite, diorite, and quartz–diorite compositions [21]. Notably, sericitization on plagioclase, uralitization on pyroxene, chloritization and epidotization on hornblende are commonly observed, particularly close to the skarn zones. The published radiometric ages for the Çelebi and the Kesikköprü granitoids are 72.9 ± 1.2 to 74.24 ± 0.66 Ma (Ar-Ar: biotite/hornblende) and 72.14 ± 0.81 to 73.41 ± 0.32 Ma (Ar-Ar: biotite/hornblende), respectively (Table 1) [8], this study. All of the aforementioned rock units were unconformably overlain by younger sedimentary rocks (Figure 2b).

Figure 2. (a) The geological map of the Kesikköprü region (modified from Akçay et al. [80]). (b) Alteration map of the Kesikköprü iron deposit and (c) geological cross—section (A–C in (b)). All abbreviations are as in Table 1. The numbers in (a,b) indicate mineralized zones: 1—Büyükocak; 2—Madentepe–II; 3—Madentepe–I; 4—Maden Geçidi; 5—Büğüz; 6—Kartalkaya; 7—Çataldere; 8—Sulu Ocak; 9—Boyalı İn; 10, 11—Camiisağır).

Figure 3. The field and petrographical characteristics of the host rocks: (a) contact between marble and dolomitic marble; (b) pyrite + chalcopyrite and calcite veinlets within marble; (c) the magnetite crystals in the foliation of marble; (d) chloritization of hornblende and clinopyroxene in the gabbro; (e) secondary calcite and quartz in the pyroxenite; (f) mafic–ultramafic rocks cut by the granitoid; (g) mineral assemblages in the monzonite; (h) relict mafic–ultramafic rocks within the granitoid; (i) garnet pockets and veins from the garnet–pyroxene (±phlogopite ± epidote) subzone; (j) contact between granitoid and mafic–ultramafic rocks; (k) phlogopite and pyroxene patch in the granitoid; (l) massive garnet from the garnet (±pyroxene ± phlogopite) subzone; (m) garnet and pyroxene from the pyroxene (±garnet ± phlogopite ± epidote) subzone; (n) epidote and garnet from the epidote–garnet subzone; (o) epidote, pyrite, and magnetite from the epidote-rich subzone.

3. Alteration

The alteration pattern in the Kesikköprü iron deposit is basically characterized by the endoskarn and exoskarn zones (Figure 2b,c). The endoskarn zone is represented by garnet–pyroxene (±phlogopite ± epidote), whereas the exoskarn zone is made of distinct mineralogic subzones. These subzones from granitoid towards the mafic–ultramafic rocks and marble are composed of garnet (±pyroxene ± phlogopite), pyroxene (±garnet ± phlogopite ± epidote), epidote–garnet, and epidote-rich mineral assemblage. These skarn zones may also contain a variety of minerals, including plagioclase, titanite, tremolite, quartz, calcite, and tourmaline.

The endoskarn zone, distinguished by garnet, pyroxene, phlogopite, and epidote, occurs in the form of pockets, veins, and veinlets within granitoids mostly conformable to the contacts between granitoid and the mafic–ultramafic rocks (Figure 2b). This mineralogical composition gives brownish, grayish, and greenish hues to the granitoid (Figure 3i–k). In this zone, garnet is the most common mineral and is brownish in color. In thin sections, it is anhedral, with medium- to coarse-grained crystals. Pyroxene, observed in greenish-gray hues, forms subhedral to anhedral crystals and exhibits slight pleochroism. This mineral forms either immediately before or simultaneously with garnet during the initial stage of skarn formation. In the endoskarn zone, pyroxene, garnet, and phlogopite were converted into tremolite, epidote, chlorite, quartz, and calcite due to retrograde reactions during the late stage of skarn formation. Phlogopite is fine-grained and greenish in color, and occurs as small veins and patches along with the varying amounts of magnetite within garnet–pyroxene-rich skarn (Figure 3k). Phlogopites, in thin sections, are often seen replaced by magnetites. Epidote is a ubiquitous mineral defining the retrograde phase and typically develops over the garnet crystals (Figure 3i). However, the presence of epidote replacing plagioclase in granitoid along with other minerals such as pyroxene and garnet may suggest, although not definitively, that epidote is formed at relatively high temperatures.

The exoskarn zone covers larger area than the endoskarn zone (Figure 2b,c). The garnet (±pyroxene ± phlogopite) subzone contains varying proportions of diopsitic pyroxene, phlogopite, and epidote, and is also characterized by the presence of medium- to coarse-grained garnet (Figure 3l). Pyroxene appears as unreplaced minerals within garnet, while epidote is commonly found within fractures traversing garnet. Phlogopites, similar to those in the endoskarn zone, occur as patches and veins and are almost always associated with magnetite. They are coarser-grained than those in the endoskarn zone and some exhibit chloritization at the edges. The pyroxene (±garnet ± phlogopite ± epidote) subzone differs from the garnet (±pyroxene ± phlogopite) subzone by the predominancy of fine-grained pyroxene (Figure 3m) and oscillatory zoned garnet in faint brown color. This subzone also contains unzoned vein-type garnets. The oscillatory zoned garnet ranges in composition from Grs₅Adr₉₅ to Grs₆₀Adr₄₀, while unzoned vein-type garnets are Grs₄₀Adr₆₀ to Grs₈₀Adr₂₀ in composition [20]. Pyroxene in this subzone has undergone significant retrograde alteration and a notable decrease in abundance toward marble and the mafic–ultramafic rocks. The epidote–garnet subzone contains less garnet and more epidote (Figure 3n). Garnets in this subzone are generally light brown, medium to coarse-grained, and mostly euhedral, whereas epidote occurs in the spaces between garnet crystals and as a transformation product on garnets. The epidote subzone has few or no garnets. Epidote in this zone is fine- to medium-grained and is often accompanied by calcite, quartz, pyrite, and magnetite (Figure 3o). They are rich in pistacite, indicating enrichment in iron during the retrograde stage of skarn formation [20].

4. Mineralization

The iron mineralization in the Kesikköprü region is found in several adjacent ore zones called Madentepe-I, Madentepe-II, Büyük Ocak, and Maden Geçidi (Figure 2b). In addition, Sulu Ocak, Boyalı İn, Camiisağır, Çataldere, Büğüz, and Kartalkaya iron deposits are also found in nearby areas (Figure 2a). These deposits were subject to intermittent mining activities in the past; however, operations have ceased due to resource exhaustion or the lack of economic viability. The Sulu Ocak and Boyalı İn deposits, considered to be continuations of each other, are characterized by hematite and limonite with lesser amounts of magnetite and pyrite [36]. The Camiisağır deposit is distinguished by extensive martitization and limonitization within karst cavities and has a proven and probable resource of 0.3 Mt at 60.81% Fe [36]. The Çataldere deposit discovered by magnetic surveys, has a resource of 0.15 Mt at 30%–50% Fe. However, it remains unoperated due to its low grade [15,37]. Büğüz, another active deposit, has an annual iron production capacity of 10,000 tons and an estimated resource of 2 Mt at 32%–64% Fe [83,85]. In this deposit, the magnetite mineralization is hosted by calcic skarn as bands and lenses within marble [83]. The Kartalkaya deposit is composed of magnetite, hematite, goethite, lepidocrocite, psilomelane, and pyrolusite, and has a probable resource of 0.9 Mt at 32% Fe, 7% S, and 3.72% MnO [38]. Recent exploration and feasibility studies have identified new resources, with an estimated 4.5 Mt of resource at 39.31% Fe for the Kartalkaya [86].

The mineralization in the Kesikköprü iron deposit is divided into two distinct types: oxide and sulfide. The oxide mineralization is represented by magnetite and hematite (±limonite), whereas the sulfide mineralization contains chalcopyrite, pyrite, and marcasite. Magnetite is present in both vein (Figure 4a) and disseminated (Figure 4b) forms in the endoskarn zone and exhibits a range of textures, including banded (Figure 4c), massive (Figure 4d), and brecciated (Figure 4e) in the exoskarn zones. Significant enrichment of massive magnetite is particularly noted in epidote–garnet and epidote exoskarn subzones, which are proximal to marble (Figure 2b and Figure 4d). Additionally, the coarse–crystalline phlogopite is also associated with massive magnetite in these zones (Figure 4f). The vein and disseminated magnetite within the endoskarn zone, as well as the banded and brecciated magnetite in the garnet- and pyroxene-rich zones of the exoskarn, are of sub-economic type, whereas massive magnetite lenses in the epidote–garnet and epidote-rich sections of the exoskarn zones form economic ore bodies. The thickness of massive magnetite lenses in the open pit area ranges from 1 to 15 m. Some of these bodies strike in the WNW–ESE direction, almost parallel to the contact between marble and granitoid (Figure 2b). Magnetite has transformed into hematite and limonite (Figure 4g,h) depending on the intensity of oxidation, especially in the upper elevation benches of the open pit. The oxidation correlates with the main strike of the faults in the open pit (Figure 2b and Figure 4h).

The sulfide mineralization occurs as veins reaching up to 3 cm in width, and occasionally traverses magnetite as very small clusters or pockets, and disseminated minerals (Figure 4i). These veins, younger than the magnetite mineralization, consist of pyrite, chalcopyrite, and minor amounts of marcasite. Sulfide-rich zones spatially correlate with the magnetite-rich zones or occur in close proximity to these zones. Sulfide veins cutting across marble are prominently associated with late-stage calcite and quartz (Figure 3b). The predominant sulfide mineral in such veins is euhedral/subhedral pyrite. Chalcopyrite is not visible with the naked eye or hand lens. It is typically identified under the microscope (Figure 4i,j). It is accompanied by pyrite with marcasite transformation in certain locations (Figure 4j,k). Malachite, resulting from the oxidation of chalcopyrite, either occurs as veins within hematite ± limonite-rich zones or is occasionally observed as coatings lining the fractures within the marble blocks in the upper benches of the open pit (Figure 4h,l). The paragenetic sequence of skarn and ore minerals is given in Figure 5.

5. Materials and Methods

5.1. Geochemistry

A total of 39 rock samples selected by petrographical examination were analyzed. Of these samples, 21 are from granitoid, 6 from mafic–ultramafic rocks, 4 from the endoskarn zone, 7 from the exoskarn zone, and 1 from magnetite ore bodies. All the samples were analyzed for major and trace elements, with an additional 14 samples for rare earth element (REE) analysis. The major and trace element analyses were conducted using a wavelength dispersive X-Ray fluorescence (Malvern Panalytical Axios WDXRF) spectrometer at the Geochemical Analyses Laboratory (JAL) of the Scientific and Technological Application and Research Center of Aksaray University (ASÜBTAM, Aksaray, Türkiye). Before the analysis, the samples were crushed, pulverized, mixed with Mikropulver Wachs C, and pressed. The analyses were carried out using a laboratory method according to certified reference materials (DTS-2b, IA-HGC, IA-MGC-A, JA-2, JGb-1, JSI-1, JSy-1, NCS DC71303, NCS DC73301, and SDC-1) supplied by Fluxana. Intra-laboratory duplicates were analyzed, and a relative percentage difference (RPD) below 5% was considered acceptable, indicating reliable duplication. The accuracy and precision of the data were checked using two certified reference materials. The REE analyses were performed at ACME Laboratories (Vancouver, BC, Canada) with an inductively coupled plasma mass spectrometer (ICP-MS). The analytical procedure followed the SO-19 standard based on the guidelines of USGS. The results of the analysis and quality control report are presented in Supplementary Table S1.

5.2. Geochronology

The ⁴⁰Ar/³⁹Ar analysis was performed on biotite separates from granodiorite and phlogopite from an iron-rich exoskarn zone at the Nevada Isotope Geochronology Laboratory (NGIL), University of Nevada (Las Vegas). The samples were wrapped in Al foil and stacked in 6 mm inside diameter sealed fused silica tubes. Individual packets averaged 2 mm thick, and neutron fluence monitors (FC-2, Fish Canyon Tuff sanidine) were placed every 5–10 mm along the tube. Synthetic K-glass and optical grade CaF₂ were included in the irradiation packages to monitor neutron-induced argon interferences from K and Ca. The loaded tubes were packed in an Al container for irradiation. The samples irradiated at the Oregon State TRIGA Reactor, Corvallis (OR, USA) were in-core for 9.1 h in the F-12 position, In-Core Irradiation Tube (ICIT) of the 1 MW TRIGA type reactor designed and manufactured by General Atomics (San Diego, CA, USA). Correction factors for interfering neutron reactions on K and Ca were determined by repeated analysis of the K-glass and CaF₂ fragments. The measured (⁴⁰Ar/³⁹Ar)_K values were 4.50 (±96.81%) × 10⁻³. The Ca correction factors were (³⁶Ar/³⁷Ar)_Ca = 2.56 (±0.32%) × 10⁻⁴ and (³⁹Ar/³⁷Ar)_Ca = 6.97 (±0.28%) × 10⁻⁴. J factors were determined by the fusion of 6–10 individual crystals of neutron fluence monitors.

The irradiated FC-2 sanidine standards, together with the CaF₂ and K-glass fragments, were placed in a Cu sample tray in a high vacuum extraction line and were fused using a 20 W CO₂ laser. The samples utilized a double vacuum resistance furnace similar to the Staudacher et al. [87] design. Reactive gases were removed by three GP-50 SAES getters prior to being admitted into an NGX multi-collector mass spectrometer by expansion. Peak intensities were measured simultaneously with m/z 40, 39, 38, and 37 measured using Faraday cups with ATONA amplifiers. The 36 m/z peak was measured using an ion-counting discrete dynode electron multiplier. All the peaks were analyzed using two-second integration times with 150 cycles, and the concentrations at the time of inlet were determined through linear regression. Mass discrimination factors (MDFs) were monitored by the repeated analysis of atmospheric argon aliquots from an online pipette system, assuming an atmospheric ⁴⁰Ar/³⁶Ar value of 298.56 [88]. All the age determinations and associated uncertainties were calculated using ArArCalc v.2.7.0 [89]. All the uncertainties are provided at the 2σ level and include errors in the data regression, baseline corrections, irradiation constants, the J curve value, mass fractionation, blanks, and post-irradiation decay of ³⁷Ar and ³⁹Ar. An age of 28.02 Ma [90] was used for the Fish Canyon Tuff sanidine fluence monitor in calculating the ages for the samples. The ages were calculated using the total ⁴⁰K decay constant of 5.530 ± 0.097 × 10⁻¹⁰ yr⁻¹ [91]. The result of the analysis is presented in Supplementary Table S2.

5.3. Radiogenic Isotope Geochemistry

Radiogenic isotope analyses (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) were performed on 10 rock samples: 4 from the granitoid rocks, 1 from the mafic–ultramafic rock, 2 from the endoskarn zone, 2 from the exoskarn zone, and 1 from magnetite ore. The isotopic composition was measured using a Thermo-Fisher Triton thermal ionization mass spectrometer (TIMS; Thermo Fisher Scientific GmbH, Erlangen, Germany)with static multi-collection at the Radiogenic Isotope Laboratory of the Central Laboratory of the Middle East Technical University in Türkiye. The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios were normalized to ⁸⁶Sr/⁸⁸Sr = 0.1194 and ¹⁴⁶Nd/¹⁴⁴Nd = 0.7219, respectively. During the analysis, the Sr standard NIST NBS 987 yielded a value of 0.710279 ± 8 (n = 2), while the Nd La Jolla standard produced a value of 0.511859 ± 3 (n = 2). Analytical uncertainties were reported at the 2σ level.

5.4. Stable Isotope Geochemistry

Stable isotope analyses (δ¹⁸O, δ²H, δ¹³C, and δ³⁴S) were performed at the Queen’s Facility for Isotope Research, Queen’s University (Kingston, ON, Canada). A total of 26 isotope analyses were carried out on 19 minerals from 11 samples. The analyses have been carried out on garnet, magnetite, calcite, pyrite, quartz, epidote, and phlogopite. The results are reported in per mil (‰) notation and calibrated against certified reference materials: Vienna Standard Mean Ocean Water (VSMOW) for δ¹⁸O and δ²H, Vienna Pee Dee Belemnite (VPDB) for δ¹³C, and Vienna Canyon Diablo Troilite (VCDT) for δ³⁴S. The analytical accuracy was reported as 0.5‰ for δ¹⁸O, 1.5‰ for δ²H, 0.1‰ for δ¹³C, and 0.2‰ for δ³⁴S. For oxygen isotope analysis in silicate and oxide minerals, oxygen was extracted from 5 mg samples at 550–600 °C using the BrF₅ method of Clayton and Mayeda [92]. The δ¹⁸O ratios were measured using a Thermo-Finnigan DeltaPlus XP Isotope Ratio Mass Spectrometer (IRMS) with a dual inlet. The δ²H isotope values of the silicate minerals were determined by degassing the samples at 100 °C for 1 h, followed by crushing and analysis using a Thermo-Finnigan thermo-combustion elemental analyzer (TC/EA) coupled with a Thermo-Finnigan DeltaPlus XP CF-IRMS. For the carbonate mineral (calcite), the δ¹³C and δ¹⁸O values were determined by reacting approximately 1 mg of powdered material with anhydrous phosphoric acid at 72 °C for 4 h. The resulting CO₂ was measured using a Thermo-Finnigan Gas Bench connected to the DeltaPlus XP Continuous-Flow Isotope Ratio Mass Spectrometer (CF-IRMS). The sulfur isotope ratios (δ³⁴S) were determined using a MAT 253 Stable Isotope Ratio Mass Spectrometer coupled with a Costech ECS 4010 Elemental Analyzer. The sulfur isotope ratios were normalized to the ³⁴S/³²S ratios of VCDT.

6. Results

6.1. Whole Rock Geochemistry

6.1.1. Host Rock

The Kesikköprü granitoid is compositionally classified as diorite, granodiorite, and granite, while the mafic–ultramafic rocks are identified as gabbro (Figure 6a). The granitoid samples, characterized by an intermediate to acidic magma, cluster within the sub-alkaline, calc-alkaline, and shoshonite fields according to the TAS, AFM, and SiO₂-K₂O diagrams. The mafic–ultramafic rocks display sub-alkaline and tholeiitic characteristics (Figure 6a–c). In the aluminum saturation diagram [93], the samples are predominantly metaluminous, except for a few that display peraluminous character (Figure 6d).

The granitoid samples are distinguished by higher SiO₂, Na₂O, K₂O, and P₂O₅, and lower MgO, CaO, Fe₂O₃, and MnO in comparison to the mafic–ultramafic rocks. The Harker diagrams for the granitoid samples exhibit a negative correlation between SiO₂ and TiO₂, Al₂O₃, MgO, CaO, Fe₂O₃, MnO, and P₂O₅, in contrast to the positive trend between SiO₂ and K₂O (Figure 7), which represents the fractional crystallization and/or the interaction between mafic and felsic magmas [21,94]. In the multi-element plots, all the granitoid samples display similar patterns and are distinguished by enrichment in Large Ion Lithophile Elements (LILEs) and High-Field-Strength Elements (HFSEs) relative to Mid-Ocean Ridge Basalt (MORB), with the exception of P, Ti, and Y (Figure 8a). The depletion of Nb and Ta relative to LILE and Ti and P relative to MORB is evident. On the other hand, the mafic–ultramafic rocks display a pattern roughly parallel to line 1, reflecting derivation from a MORB-related source. They are characterized by slightly higher abundances of LILE, particularly K, Rb, and Ba, and lower (Zr and Ti) abundances of HFSE relative to MORB. Additionally, they have a lower enrichment ratio of incompatible elements compared to the granitoid samples (Figure 8a). The chondrite-normalized REE patterns for all the host rock units indicate an enrichment of light REE (LREE) over heavy REE (HREE) (Figure 8b). The degree of enrichment in LREE relative to HREE is relatively lower in the mafic–ultramafic rocks compared to granitoid. Furthermore, all the host rock samples exhibit a notable flattening of HREE relative to LREE. The granitoid samples also display a depletion in Eu, with a (Eu/Eu*)_N ratio between 0.53 and 0.77.

In the tectonic discrimination diagrams of Pearce et al. [95], all the samples from granitoid plot predominantly in the VAG field and in close proximity to the triple junction with syncollisional (syn-COLG), within-plate granite (WPG), and volcanic arc granite (VAG) (Figure 9a,b). As highlighted by Pearce [96], this geochemical signature is commonly associated with a post-collisional geodynamic setting (Figure 9a). This characteristic is also noted in the R₁ versus R₂ diagram of Batchelor and Bowden [97] and in the Hf-Rb/30-3*Ta ternary diagram of Harris et al. [98] (Figure 9c,d).

Figure 6. (a) SiO₂ vs. Na₂O + K₂O diagram [99]; (b) AFM diagram [100]; (c) SiO₂ vs. K₂O diagram [101]; (d) Al₂O₃/CaO + Na₂O + K₂O (A/CNK) vs. Al₂O₃/Na₂O + K₂O (A/NK) [93]. The geochemical data of the Çelebi granitoid were taken from Bayhan [21], İlbeyli et al. [69], and Kuşcu et al. [82].

Figure 7. Harker diagrams illustrating the relationship between SiO₂ and major oxide elements. The geochemical data of the Çelebi granitoid were taken from Bayhan [21], İlbeyli et al. [69], and Kuşcu et al. [82].

Figure 8. (a) MORB and (b) chondrite normalized spider diagrams (MORB and chondrite data are taken from Pearce [102] and Boynton [103], respectively. The geochemical data of the Çelebi granitoid were taken from Bayhan [21], İlbeyli et al. [69], and Kuşcu et al. [82].

Figure 9. Tectonomagmatic discrimination diagrams: (a) Y + Nb vs. Rb; (b) Ta + Yb vs. Rb (ORG: Ocean Ridge Granite; post-COLG: Post-Collision Granitoid; Syn-COLG: Syn-Collision Granite; VAG: volcanic arc granite; WPG: within-plate granite) [95,96,104]; (c) R₁ vs. R₂ (1: Anorogenic; 2: Late-orogenic; 3: Post-collision Uplift; 4: Pre-plate collision; 5: Mantle fractionates; 6: Syn-collision; 7: Post-orogenic) [97]; and (d) Hf-Rb/30-3*Ta [98]. The geochemical data of the Çelebi granitoid were taken from Bayhan [21], İlbeyli et al. [69], and Kuşcu et al. [82].

6.1.2. Skarn

Harker diagrams demonstrate a decrease in SiO₂, TiO₂, Al₂O₃, Na₂O, K₂O, and P₂O₅ and an increase in CaO, Fe₂O₃, and MnO from granitoid through the endoskarn and exoskarn zones to the magnetite ore (Figure 7). The elements in the samples from the endoskarn zone are more closely aligned with those of the granitoid samples compared to the exoskarn zone and magnetite ore samples (Figure 8). All the endoskarn zone samples exhibit the depletion in Ti and Y, whereas most exoskarn zone samples are characterized by depletion in Sr, K, Rb, Ba, P, Zr, Ti, and Y relative to MORB. The sample from magnetite ore shows a depletion for all the trace elements except Th (Figure 8a).

All the skarn and ore samples are enriched in LREE relative to HREE in the chondrite-normalized REE diagram (Figure 8b). This diagram also shows that the samples from granitoid and endoskarn exhibit similar patterns. The REE patterns of the skarn and ore samples are demonstrated with a positive Eu anomaly, with the exception of one endoskarn sample. The (Eu/Eu*)_N ratios for the two endoskarn samples are 0.70 and 1.12, while those of the two exoskarn samples are 1.14 and 3.43. The ratio for the magnetite ore sample is 1.18.

6.2. Ar/Ar Geochronology

Ar-Ar analyses were carried out on separates of biotite from granodiorite (Sample no: KK-20-01) and phlogopite from a magnetite-rich skarn sample (Sample no: KK-18-14). The phlogopite did not yield a reliable plateau due to its low potassium content, likely caused by chloritization. No fresh amphibole within the granodiorite was available for analysis due to pervasive alteration, despite selecting the freshest field sample. The biotite separates, on the other hand, had a large spike of excess argon in the middle of the heating spectrum, resulting in high apparent ages (Figure 10; 73.83 ± 0.04 Ma with MSWD of 42). Nonetheless, there is neither an isochron with sufficiently low MSWD (<2.5) nor >5 consecutive heating steps [105]. The total fusion age for this biotite sample is 73.41 ± 0.32 Ma (Figure 10). These total fusion and plateau ages are statistically similar and consistent with previously published Ar/Ar age data, including 72.14 ± 0.81 Ma (hornblende from granodiorite) for the Kesikköprü granitoid, 74.24 ± 0.66 Ma (biotite from sericitized aplite dyke), 72.9 ± 1.2 Ma (hornblende from granodiorite), and 73.69 ± 0.41 Ma (biotite from granodiorite–quartz monzonite) for the Çelebi granitoid [8].

6.3. Radiogenic Isotopes

The ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotope values obtained from the host rocks and alteration–mineralization zones range between 0.707964 and 0.711355 and 0.512161–0.512498, respectively (Table 2). Two out of ten samples (KK-16-02 and KK-16-06) did not yield the ⁸⁷Sr/⁸⁶Sr value, likely due to their low Sr contents. The initial Sr and Nd isotope ratios, as well as the εSr_i and εNd_i values for both the granitoid and skarn samples, were calculated using the age of the Kesikköprü granitoid (73.41 ± 0.32 Ma) due to the lack of age data for the alteration and mineralization, while a plagiogranite age from the Ankara mélange was used for the mafic–ultramafic rock sample (179 ± 0.15 Ma) [106]. The calculated initial εNd and εSr values were evaluated on the isotope correlation diagram, which shows the positions of various source regions corresponding to different tectonic environments (Figure 11a,b). All of the samples were situated in the enriched quadrant of the isotope correlation diagram. According to the Nd- and Sr-isotope values plotted against the AnalyzerSm/Nd and Rb/Sr ratios, respectively, the granitoid samples exhibit nearly horizontal trends indicating the fractional crystallization event during magma ascent [66,107]. Otherwise, crustal contamination would typically produce positive and negative trends in the (⁸⁷Sr/⁸⁶Sr)_i vs. Rb/Sr and (¹⁴³Nd/¹⁴⁴Nd)_i vs. Sm/Nd plots, respectively (Figure 11c,d). The initial isotope values of the skarn samples nearly overlap with those of the granitoid samples. A clear decrease in the Rb/Sr ratio and a slight modification of the Sm/Nd ratio shows the alteration effect in the skarn samples, also pointing to the lower mobility of Sm/Nd than Rb/Sr (Figure 11c,d).

Figure 11. (a,b) Isotope correlation diagram. The isotopic reservoirs were taken from Rollinson [107], Zindler and Hart [108], and Faure [109]; BE: Bulk Earth, DM: Depleted Mantle, EMI: Enriched Mantle I, HIMU: High Mantle U/Pb ratio, MORB: Mid-Ocean Ridge Basalt, OIB: Ocean Island Basalt). (c) Sm/Nd vs. (¹⁴³Nd/¹⁴⁴Nd)_i; (d) Rb/Sr vs. (⁸⁷Sr/⁸⁶Sr)_i diagram. The radiogenic isotope data of the Çelebi granitoid were taken from İlbeyli et al. [69].

6.4. Stable Isotopes

The δ¹⁸O values of skarn minerals (garnet, magnetite, calcite, quartz, epidote, and phlogopite) range from −0.7 to 26.9‰, while the δ²H values are between −67 and −51‰ (Table 3). The temperature estimates derived from the calc-silicate mineral pairs (calcite–garnet, calcite–phlogopite, quartz–magnetite, and calcite–epidote) range from 405 °C to 574 °C, with the exception of a temperature of 123 °C from the calcite–chalcedony quartz mineral pair in a late-stage vein (Table 3). The calculated δ¹⁸O_fluid and δ²H_fluid values (‰) of the minerals range from 2.32 to 18.22 and from −52.10 to −15.10, respectively. The δ¹⁸O_fluid and δ²H_fluid values of the phlogopite separates fall within the magmatic water field, whereas those of epidote separate plot close to the metamorphic water field trending toward higher δ²H values (Figure 12). A decrease in the δ¹⁸O_fluid values from phlogopite (528 °C) to epidote (462 °C) approaching the meteoric water line might indicate the attenuation of the magmatic component in the hydrothermal fluid, whereas garnets (574 °C) do not exhibit a regular balance. These δ¹⁸O_fluid values are mostly consistent with those from other well-known skarn deposits and their associated granitoids [110,111,112,113,114,115,116].

The δ¹³C values of the calcite samples exhibit a range of −6.7 to 0.8‰, with the three samples specifically varying between −0.7 and 0.8‰. The δ¹⁸O values of calcites range from 7.1 to 24.2‰, with the three samples exhibiting a variation between 7.1 and 10.1‰. These are consistent with those found in the skarn deposits where carbon isotopes often reflect a mix of magmatic and marine carbonate sources (−11.6 to 5.3‰ for δ¹³C; −2.4 to 29.8‰ for δ¹⁸O) [30,83,111,115,117]. The relatively narrow range of the δ¹⁸O_fluid values (5.05 to 6.57‰), except for one sample in a late-stage vein (KK-14-04; 8.66‰), shows that calcite is formed by an isotopically homogeneous fluid.

The δ³⁴S values of pyrites from the Kesikköprü iron deposit range from 4.5 to 7.8‰, with a mean value of 6.3‰. These isotopic values coincide with those commonly found in granitic rocks (−10 to +15‰) [118]. These values are also comparable to those of the primitive mantle and similar to the δ³⁴S values of pyrites reported in several skarn deposits of Türkiye (−4.8 to 15.6‰) [30,112,113,115,116].

Table 3. The results of stable isotope analyses.

Sample No	Explanation	Mineral	δ¹⁸O ‰	δ²H ‰	δ¹³C ‰	δ³⁴S ‰	Mineral Pairs (Temperature, °C) *	Used T (°C) in Calculations	Calculated δ¹⁸O_fluid ‰ **	Calculated δ²H_fluid ‰ ***
			VSMOW	VSMOW	VPDB	VCDT	Mineral Pairs (Temperature, °C) *	Used T (°C) in Calculations	Calculated δ¹⁸O_fluid ‰ **	Calculated δ²H_fluid ‰ ***
KK-16-01	Magnetite ore	Grt	15.2					574	18.22
KK-16-02	Exoskarn (Grt ± Px ± Phl)	Grt	3.3				Cal_KK-18-06-Grt_KK-16-02 (574 °C)	574	6.32
KK-18-01	Exoskarn (Ep − Grt)	Grt	−0.1					574	2.92
		Mag	3.5					517	10.37
		Cal	7.8		0.01		Cal_KK-18-01-Ep_KK-18-07 (462 °C)	462	5.05
KK-18-02	Sulfide Phase	Py				6.5
KK-18-04	Late-stage Cal-Qz Vein	Cal	24.2		−6.7		Qz_KK-18-09-Cal_KK-18-04 (123 °C)	123	8.66
KK-18-05	Exoskarn (Px ± Grt ± Phl ± Ep)	Grt	−0.7					574	2.32
		Mag	5.2				Qz_KK-18-05-Mag_KK-18-15 (517 °C)	517	12.07
		Qz	11.0					405	6.58
		Cal	10.1		0.8		Qz_KK-18-05-Cal_KK-18-05 (405 °C)	405	6.57
KK-18-06	Exoskarn (Grt ± Px ± Phl)	Cal	7.1		−0.7			574	5.31
KK-18-06		Py				4.5
KK-18-07	Exoskarn (Ep − Grt)	Ep	4.9	−51				462	5.74	−15.10
KK-18-07		Py				7.8
KK-18-09	Late-stage Cal-Qz Vein	Qz	26.9					123	8.73
KK-18-14	Exoskarn (Px ± Grt ± Phl ± Ep)	Phl	6.3	−67				528	8.67	−52.10
KK-18-15	Exoskarn (Px ± Grt ± Phl ± Ep)	Phl	6.5	−64			Cal_KK-18-05-Phl_KK-18-15 (528 °C)	528	8.87	−49.10
KK-18-15		Mag	2.9					517	9.77

Abbreviations: Cal: calcite; Ep: epidote; Grt: garnet; Mag: magnetite; Phl: phlogopite; Py: pyrite; Px: pyroxene; Qz: quartz; * the calculated temperature values (°C) were derived from mineral pairs the based on fractionation factors from Zheng [119] for Cal-Grt; Zheng [120] for Cal-Phl and Cal-Ep; Zheng [121] for Qz-Mag; and Zheng [122] for Qz-Cal. ** the calculated fluid compositions (δ¹⁸O_fluid) were based on fractionation factors from Zheng [119] for Grt and Qz; Zheng [120] for Phl and Ep; Zheng [121] for Mag; and Zheng [122] for Cal. *** the calculated fluid compositions (δ²H_fluid) were based on fractionation factors from Suzuoki and Epstein [123] for Phl; and Graham et al. [124] for Ep.

Figure 12. δ¹⁸O_fluid vs. δ²H_fluid diagram and the isotope contents of some skarn minerals and skarn-related granitoids (pink dashed rectangles). The data for the water types were taken from Rollinson [109], Epstein et al. [125,126], Sheppard [127,128], and Taylor [129], whereas the data for pink dashed lines are from Meinert et al. [110], Orhan et al. [111], Oyman et al. [112], Oyman [113], Öztürk and Helvaci [114], Sipahi et al. [115], and Yılmazer et al. [116].

7. Discussion

7.1. Temporal Relationship Between the Kesikköprü Granitoid and Mineralization, and Constraints on Other Magmatic–Hydrothermal Systems

In the CACC, skarn and porphyry-Cu type systems are associated with H-type magmatism that primarily peaked during the Late Cretaceous and Middle Eocene [8,58,82,130,131]. Middle Eocene Karamadazı granitoid in the south of CACC (Figure 1c) is linked to an Fe-skarn deposit that has recently revealed a porphyry-Cu potential based on alteration mineralogy and metal content [132,133]. Late Cretaceous is mainly characterized by Fe-Cu ± Au, Fe, Fe-W, Mo, and Cu-Mo deposits and is defined as a belt extending from Sivas in the northeast through Yozgat in the north and Kırıkkale in the northwest [8,11]. In the northwestern and northern parts of the CACC, the age of magmatism associated with Fe and Fe-W skarn (Çelebi), Pb-skarn (Keskin), and porphyry Cu-Mo deposits (Karacaali, Balışeyh, and Başnayayla) is between 71 and 79 Ma, while their alteration and mineralization ages are from 70 to 78 Ma [8,134,135,136]. In the northeastern part of the CACC, magmatism, associated with iron oxide–copper–gold (IOCG) systems, is regarded as a member of the post-collisional alkaline rock assemblage with age constraints ranging from 62 to 79 Ma in Divriği-Sivas and 71–77 Ma in Hasançelebi-Hekimhan [26,29,32]. In addition, the ages of alteration and mineralization in the A-Kafa (Divriği) and Hasançelebi (Hekimhan) deposits are 73–75 Ma and 68–75 Ma, respectively [26,30,32]. The skarn and porphyry Mo-Cu fertility in the CACC spans approximately 70 to 77 Ma [8], comparable to the yielded biotite age from the Kesikköprü granitoid (73.41 ± 0.32 Ma; Figure 10). The Ar-Ar dating of biotite represents the cooling age of the intrusion below ~300 °C. Since the age of alteration–mineralization could not be determined from phlogopite due to retrograde alteration, it is reasonable to infer that mineralization occurred synchronously with or shortly after granitoid emplacement, during the cooling and hydrothermal fluid evolution phase. Therefore, the Ar-Ar biotite age provides an upper constraint on the timing of mineralization. Reliable age constraints from skarn-related minerals (e.g., U-Pb in garnet and Re-Os in sulfide) are required to refine the precise timing of the Kesikköprü iron deposit.

Considering the Late Cretaceous, porphyry-Cu, and IOCG systems in the CACC [8,136], associated with the post-collisional magmatism following continental collision between the Pontides (active margin of the Eurasian plate) and the Tauride–Anatolide block (passive continental margin of the Gondwanaland), the spatio-temporal data presented herein suggest that the Kesikköprü granitoid might also have upside potential for the porphyry-Cu and IOCG deposits. In the CACC, some authors consider Fe ± Cu skarn deposits to have potential for IOCG and porphyry-Cu mineralization [8,24,28,32]. However, the lack of widespread sodic and potassic alteration, paucity of the metal variety, its small size, and being away from the main structural zones put constraints against the IOCG potential. In addition, some mineralogical and petrographic characteristics of the Kesikköprü granitoid—such as its equigranular texture, the absence of successive magmatic pulses and related alteration patterns, stockwork, and vein systems, as well as its Cu-deficient metal content—limit its porphyry-Cu potential. Moreover, the δ³⁴S values of pyrites in the Kesikköprü iron deposit (Table 3) are slightly higher than those values of sulfide minerals from porphyry-Cu deposits (−3 to +1‰) [109,137].

7.2. Tectonic Setting and Petrogenesis of the Kesikköprü Granitoid

In the Kesikköprü region, mineralization displays close spatial association with the Kesikköprü granitoid (Figure 2). Kesikköprü granitoid, consisting of diorite, granodiorite, and granite in composition, is derived from a hybrid magma source generated by the mingling and mixing of coeval mafic and felsic magmas, as in all of the central Anatolian H-type granitoids [21,65,82,130,138]. In the CACC, less differentiated granitoids, with a lower contribution from the crust, exhibit greater iron potential, and they are more fertile, whereas the more felsic, leucocratic, and differentiated granitoids are less fertile for iron [82,84]. The Kesikköprü granitoid, ascribed as the southern extension of the Çelebi granitoid in the study area, predominantly comprises more mafic and less differentiated rocks, whereas the Çelebi granitoid exhibits a bimodal composition, including more differentiated sections. In this context, the Kesikköprü granitoid samples have higher concentrations of TiO₂, MgO, CaO, Fe₂O₃, and P₂O₅ along with lower Na₂O and SiO₂ contents compared to the Çelebi granitoid (Figure 6 and Figure 7). In the Kesikköprü granitoid, the presence of K-feldspar megacrystals, leucocratic and mesocratic types of rocks, and the rounded and sharp-edged monzonite, monzodiorite, diorite, and quartz–diorite enclaves are considered as the involvement of mantle material or mixing/mingling processes formed between mafic and felsic magmas [21,82].

The depletion of Ta and Nb (relative to LILE), and P, Ti, and Y (relative to MORB) with enrichment of Rb, Ba, and Th, indicates an inheritance from earlier subduction in the mantle and/or crustal contamination in the formation of granitoid [21,69,70,82]. As shown in the tectonomagmatic discrimination diagrams (Figure 9), the granitoid sample plot in the VAG region and are located close to the triple junction where VAG, syn-COLG, and WPG types converge. This region is characterized by the geochemical features of most post-collisional calc-alkaline granitoids in the CACC [139]. The arc-related geochemical features of granitoids in a post-collisional environment mostly originate from mantle modified by subduction-related processes such as the addition of elements from the slab and/or mantle wedge interaction [97,100]. All the samples from the granitoid show similar REE patterns which are defined by a substantial flattening of HREE relative to LREE, and the negative Eu anomaly that might indicate crustal contamination and feldspar and/or plagioclase fractionation, respectively (Figure 8b). This might also be due to the interaction between melt and meta-pelitic rocks during the emplacement of intrusive rocks [113]. The higher Th/Yb (11.01 to 21.38) and Ta/Yb (0.25 to 0.79) ratios in the Kesikköprü granitoid, compared to MORB, support a mantle source metasomatized by a subduction process. A slightly high Sr/Y ratio (between 10.9 and 33.7) and SiO₂ value (>59%) (Supplementary Table S1) may also suggest the derivation of the arc magma and adakite-like nature of the Kesikköprü granitoid, which strengthens the possibility of a porphyry-Cu type mineralization in the deep parts of the Kesikköprü granitoid as claimed by Kuşcu [24] and Kuşcu et al. [8]. However, certain mineralogical and petrographic characteristics, along with the absence of metal content and an alteration pattern as discussed in Section 7.2, provide evidence against this interpretation—at least in the Kesikköprü area. The radiogenic isotope composition of the Kesikköprü granitoid is represented by high initial Sr and low Nd isotope values (Figure 11), suggesting either crustal contamination and/or metasomatized mantle source in its formation, as indicated by trace element and tectonomagmatic discrimination diagrams (Figure 9). All the geochemical characteristics of the samples suggest that the Kesikköprü granitoid originated from a metasomatized mantle formed by partial melting in a post-collisional environment with crustal thickening and later acquired its final composition through crustal contamination and magma mingling/mixing processes, as well as fractional crystallization process during magma ascent.

7.3. Physico-Chemical and Isotopic Constraints on the Skarn Formation

The iron mineralization in Kesikköprü, mostly located at the marble front and within exoskarn, is tightly associated with five distinct mineralogical assemblages comparable to those observed in iron skarns worldwide [140]. These assemblages characterized dominantly by garnet, pyroxene, and epidote minerals, can also be mineralogically classified as early-stage prograde (e.g., garnet and pyroxene) and relatively late-stage retrograde (e.g., epidote and calcite) alterations. The transition between prograde “high-temperature” and retrograde “low-temperature” alteration can only be marked by phlogopite formation in the field and seems crucial for the massive magnetite deposition. However, it should be noted that such a distinction is based solely on mineralogical evidence. The δ¹⁸O thermometry suggests a temperature range starting from 574 °C (garnet) through 528 °C (phlogopite) and 517 °C (magnetite) to 462 °C (epidote) during the skarn formation. This temperature range (462–574 °C) does not allow the mineral paragenesis to be discriminated simply as “high temperature” or “low temperature” for the Kesikköprü deposit, suggesting that alteration and mineralization occurred within a narrow temperature range. The close paragenetic relationship between magnetite with phlogopite and the higher abundance of massive magnetite mineralization in the epidote–garnet and epidote-rich exoskarn subzones indicate that magnetite occurs at temperatures between 462 °C and 528 °C. According to Bayhan [20], the skarn formation in the Kesikköprü region was initiated by the influx of high-CO₂ hydrothermal fluids at temperatures not exceeding 675 °C and was followed by the introduction of low-CO₂ hydrothermal fluids, with temperatures below 460 °C. These values are also consistent with the reported homogenization temperature range (410 to >600 °C) for the magnetite mineralization in the Kaman Fe-skarn deposit located 5 km northeast of the Kesikköprü iron deposit [83]. The fact that the δ¹⁸O_fluid and δ²H_fluid values of phlogopite fall within the magmatic water field and the narrow temperature range from mineral pairs may indicate that even hydrous minerals of the Kesikköprü deposit, such as epidote and phlogopite, were formed from the hydrothermal fluids probably derived from magmatic source at relatively high temperature [140,141,142]. In addition, the δ¹⁸O_fluid and δ²H_fluid value of epidote (Figure 12) is displaced from the magmatic water field toward the meteoric water line, probably implying a contribution from or mixing with meteoric water without temperature change. The consistency in trace and REE patterns between the granitoid and endoskarn samples shows that they did not undergo exchange reactions with other possible fluids, aside from magmatic fluids during the formation of the endoskarn alteration [32]. It is also worth mentioning that the Sr-Nd isotope composition of the samples from the alteration zones overlaps with that of the Kesikköprü granitoid, suggesting a genetic link between the granitoid and the hydrothermal fluid responsible for alteration and mineralization. This link is further supported by the δ³⁴S values of pyrite (4.5 to 7.8‰), which fall within the sulfur isotope range of granitic rocks from Europe and Japan (−11 to +9 in granites) [107,109]. The narrow range of the δ³⁴S values in the Kesikköprü iron deposit implies a relatively uniform sulfur isotope composition, likely reflecting consistent conditions during sulfide mineralization. All the findings indicate that the magnetite mineralization formed from hydrothermal fluids associated with magmatic activity within a narrow temperature range (462–528 °C). In the last phase, the introduction of meteoric fluid(s) with lower temperatures causes the temperature to decrease to 123 °C in a late-stage calcite–quartz vein, which is consistent with the late-phase quartz–calcite–pyrite formation in the Kaman Fe-skarn deposit (171–392 °C) [83]. All these suggest that the magmatic-dominant fluid was effective in the initial phases and meteoric fluid in the later phases.

The primary ore mineral in the Kesikköprü deposit is magnetite, which occurs mainly in massive form, with lesser occurrences of banded, vein, disseminated, and brecciated textures. Hematite and limonite are also present but less abundant and represent a late and/or supergene origin. The deposit exhibits a relatively low sulfide mineral content (<2 volume percent), with pyrite being the dominant sulfide mineral. This observation aligns with the sulfide-poor nature of the skarn systems in the CACC, such as the Kaman and Çelebi Fe-skarn deposits [25,83], though some, like the Hasançelebi (Malatya) and Divriği (Sivas) Fe-Cu ± Au-rich deposits [28,30,32], contain chalcopyrite and bornite, indicating regional variations in sulfidation/oxidation potential and/or copper availability and fluid composition. Copper enrichment in the Fe-skarn deposit can be attributed to several key geological and geochemical factors that differentiate it from other Fe-skarn deposits with higher sulfide concentrations. The composition of hydrothermal fluids, particularly their copper content, is crucial, as magmas and/or protoliths of skarn enriched in copper contribute to higher chalcopyrite formation. The oxidation state also plays a significant role: reduced condition favors the loss of chalcophile elements through sulfide precipitation during cooling and crystallization, whereas highly oxidized condition promotes the retention of chalcophile elements in solution, likely due to sulfur being present as sulfate rather than as H₂S or HS⁻. The predominancy of garnet over pyroxene, along with the andraditic and diopsidic calc-silicate minerals in skarns in the Kesikköprü iron deposit, might indicate that the hydrothermal fluids are oxidized and acidic as in the Kaman Fe-skarn deposit [83]. Temperature (mostly < 450 °C) [143,144,145] and pressure conditions influence the solubility, transport, and deposition of copper. In addition, fluid saturation with respect to copper, along with the sulfidation potential of the system—often triggered by sulfate reduction via reactions between Cu-bearing fluids and early-formed magnetite—are critical controls on copper deposition. Although this study did not provide complete information on the copper saturation and sulfidation potential of the Kesikköprü mineralization, it does include data on the temperatures of the Fe-rich skarn phases in the region. In the Kesikköprü iron deposit, as well as the Kaman Fe-skarn deposit, the temperature of skarn formation, which is mostly greater than 450 °C, limits the copper formation especially in the high-temperature phases, while high-temperature fluids may keep copper in solution rather than precipitating it. However, the later phases (<460 °C; sulfide bearing late-stage calcite–quartz vein) of the Fe and Fe-W deposits related to the Kesikköprü and Çelebi granitoids are associated with Cu, Au, Ag, and As enrichment reaching up to 1%–2%, 1500 ppb, 17 ppm, and 2777 ppm, respectively [36,39,82,83]. These values are considered anomalous when compared to skarn deposits worldwide, which are typically around 100 ppm for Cu, 75 ppb for Au, 5 ppm for Ag, and 50 ppm for As [146,147]. Furthermore, the geochemical characteristics of the Çelebi and Kesikköprü granitoids, along with the mineral chemistry of pyroxene and garnet [20], align with those of global Cu and partially Au skarns [76,82]. Therefore, the Kesikköprü and Çelebi regions should be considered for further Cu and Au exploration.

8. Conclusions

The Kesikköprü iron deposit is a typical skarn mineralization generated by the Kesikköprü granitoid into CAM and CAO. The Kesikköprü granitoid has calc-alkaline, metaluminous to peraluminous, and shoshonitic nature, and is characterized by being more mafic and less differentiated compared to the Çelebi granitoid. Geochemical and isotopic signatures of Kesikköprü granitoid highlight its potential for skarn mineralization and also imply an inheritance from an earlier subduction process and/or crustal contamination, together with a fractional crystallization process during magma ascent.

The Kesikköprü iron deposit is a typical Fe-skarn with an alteration assemblage consisting of garnet–pyroxene (±phlogopite ± epidote) in the endoskarn zone and zoned pattern of calc-silicate minerals from granitoid to mafic–ultramafic rocks and marble as garnet (±pyroxene ± phlogopite), pyroxene (±garnet ± phlogopite ± epidote), epidote–garnet, and epidote-rich subzones. The mineralization in the deposit predominantly hosted by the exoskarn zones is represented by magnetite and hematite (±limonite) as the oxide-rich phase and chalcopyrite, pyrite, and marcasite as the sulfide-rich phase. Massive magnetite especially prevalent in the center of the open pit is characterized by phlogopite formation marking significant temperature changes for the magnetite deposition. δ¹⁸O thermometry reveals a narrow temperature range (462–574 °C) for the magnetite mineralization, challenging the simple classification into “high” or “low” temperature processes. Geochemical characteristics and stable (¹⁸O, ²H, and ³⁴S) and radiogenic isotope (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) data indicate that the hydrothermal fluid responsible for the alteration and mineralization is sourced from magma that also produced the granitoids in the deposit.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min15050528/s1, Table S1: The geochemical results of the host and altered rocks in the Kesikköprü iron deposit; Table S2: ⁴⁰Ar/³⁹Ar dating result of biotite from the granodiorite.

Author Contributions

Conceptualization, methodology, investigation, writing—original draft, writing—review and editing, visualization (E.Y. and M.H.T.), and supervision (E.Y.). All authors have read and agreed to the published version of the manuscript.

Funding

This study has been supported by the Research Fund of Aksaray University (Project numbers: 2013-079, 2015-028, and 2018-009).

Data Availability Statement

All data are included in the manuscript and Supplementary Materials.

Acknowledgments

This study is a part of the M.Sc thesis of the second author. The authors express their gratitude to Özce and Güncem Mining Companies for providing logistical support during the field studies. Special thanks are extended to İlkay Kuşcu for a constructive review of the first draft of the manuscript. We are especially grateful to Kathleen Zanetti and Kevin Konrad for their helpful comments and assistance with the Ar-Ar analyses. The authors gratefully acknowledge the three anonymous reviewers for their valuable comments, which helped improve the quality and clarity of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations, including mineral abbreviations as defined by Warr [148], are used in this manuscript.

Act	Actinolite	JAL	Geochemical Analyses Laboratory
AKM	Akdağmadeni Massif	Lim	limonite
Ab	Albite	LREE	light REE
Adr	Andradite	Mlc	malachite
ALKOS	silica-oversaturated alkaline plutons	Mrc	marcasite
ALKUS	silica-undersaturated alkaline plutons	Kfs	K-feldspar
Amp	amphibole	KM	Kırşehir Massif
ASÜBTAM	Scientific and Technological Application and Research Center of Aksaray University	LILE	Large Ion Lithophile Element
Ba	Barite	MM	Menderes Massif
BE	Bulk Earth	MORB	Mid-Ocean Ridge Basalt
CACC	Central Anatolian Crystalline Complex	Mag	magnetite
CAG	Central Anatolian Granitoids	MTA	General Directorate of Mineral Exploration and Research
CAM	Central Anatolian Metamorphics	NGIL	Nevada Isotope Geochronology Laboratory
CAO	Central Anatolian Ophiolites	NM	Niğde Massif
Cal	calcite	OIB	Ocean Island Basalt
CEASs	central-eastern Anatolian alkaline syenitoids	ORG	Ocean Ridge Granite
CF-IRMS	Continuous-Flow Isotope Ratio Mass Spectrometer	Pent	Pentlandite
CP	Central Pontide	Phl	phlogopite
Ccp	chalcopyrite	Post-COLG	Post-Collision Granitoid
DM	Depleted Mantle	Py	pyrite
DSF	Dead Sea Fault	Px	pyroxene
EFZ	Ecemiş Fault Zone	Qz	quartz
EMI	Enriched Mantle I	REE	rare earth elements
EP	Eastern Pontide	RSZ	Rhodope–Strandja Zone
Ep	epidote	Scp	Scapolite
Fl	Flourite	Sch	Scheelite
Gth	goethite	Se	sericite
Grt	garnet	Spc	Specularite
Grs	Grossular	Syn-COLG	Syn-Collision Granite
Gt	billion metric tons	SZ	Sakarya Zone
Hem	hematite	TB	Thrace Basin
HFSE	High-Field-Strength Element	TC/EA	Thermo-Combustion Elemental Analyzer
HIMU	High Mantle U/Pb ratio	TGFZ	Tuz Gölü Fault Zone
HREE	heavy REE	TIMS	thermal ionization mass spectrometer
IAESZ	İzmir–Ankara–Erzincan Suture Zone	Ttn	titanite
ICIT	In-Core Irradiation Tube	Tr	tremolite
ICP-MS	inductively coupled plasma mass spectrometer	VAG	volcanic arc granite
IOCG	iron oxide–copper–gold	VCDT	Vienna Canyon Diablo Troilite
IPS	Intra-Pontide Suture	VPDB	Vienna Pee Dee Belemnite
IRMS	Isotope Ratio Mass Spectrometer	VSMOW	Vienna Standard Mean Ocean Water
ITS	Inner-Tauride Suture	WDXRF	wavelength dispersive X-Ray fluorescence
IZ	Istanbul Zone	WPG	within-plate granite

References

Tuck, C.C. Iron ore. In 2018 Minerals Yearbook; U.S. Department of the Interior, U.S. Geological Survey: Reston, VA, USA, 2021; pp. 39.1–39.11. [Google Scholar]
Statista. Global Usable Iron Ore Production 2010–2024. Available online: https://www.statista.com/statistics/589945/iron-ore-production-gross-weight-worldwide/ (accessed on 8 April 2025).
Cihnioğlu, M.; İşbaşarır, O.; Ceyhan, Ü.; Adıgüzel, O. Türkiye Demir Envanteri; MTA Publication: Ankara, Türkiye, 1994; pp. 1–408. (In Turkish) [Google Scholar]
Hastorun, S. The mineral industry of Turkey. In 2014 Minerals Yearbook (Turkey); U.S. Department of the Interior, U.S. Geological Survey: Reston, VA, USA, 2016; pp. 46.1–46.26. [Google Scholar]
General Directorate of Mineral Research and Exploration (MTA). Türkiye Yer Altı Kaynakları (İllere göre); Yer Bilimleri ve Kültür Serisi-5; MTA Publication: Ankara, Türkiye, 2009; pp. 1–602. (In Turkish) [Google Scholar]
General Directorate of Mining and Petroleum Affairs (MAPEG). Mineral Production Statistics in Türkiye. Available online: https://www.mapeg.gov.tr/Sayfa/Madenistatistik (accessed on 8 April 2025).
State Planning Organization of Türkiye (DPT). Madencilik Özel İhtisas Komisyonu Raporu Metal Madenler Alt Komisyonu Demir Çalışma Grubu Raporu. In Sekizinci Beş Yıllık Kalkınma Planı; DPT Publication: Ankara, Türkiye, 2001; pp. 1–59. (In Turkish) [Google Scholar]
Kuşcu, İ.; Tosdal, R.M.; Gençalioğlu-Kuşcu, G. Episodic porphyry Cu (-Mo-Au) formation and associated magmatic evolution in Turkish Tethyan collage. Ore Geol. Rev. 2019, 107, 119–154. [Google Scholar] [CrossRef]
Okay, A.İ.; Tüysüz, O. Tethyan sutures of northern Turkey. Geol. Soc. Lond. Spec. Publ. 1999, 156, 475–515. [Google Scholar] [CrossRef]
Erler, A.; Bayhan, H. Mineral Deposits Related with Central Anatolian Granitoids. In Proceedings of the Ofiyolit-Granitoyid İlişkisi ile Gelişen Demir Yatakları Sempozyumu, Sivas, Türkiye, 10–13 September 1998; pp. 83–96. [Google Scholar]
Kuşcu, İ.; Erler, A. Mineralization events in a collision related setting: The Central Anatolian Crystalline Complex. Int. Geol. Rev. 1998, 40, 552–565. [Google Scholar] [CrossRef]
Genç, Y.; Yürür, M.T. Savcılıebeyit (Kaman-Kırşehir) gold mineralization and its genetic relationship with post-collisional exhumation and extensional tectonics in Central Anatolia, Turkey. Yerbilimleri 2018, 39, 155–176. [Google Scholar] [CrossRef]
Göncüoğlu, M.C.; Toprak, V.; Kuşcu, İ.; Erler, A.; Olgun, E. Orta Anadolu Masifinin Batı Bölümünün Jeolojisi, Bölüm 1: Güney Kesim; Report No: 2909; TPAO Publication: Ankara, Türkiye, 1991. (In Turkish) [Google Scholar]
Özce Mining Company. Iron Ore Production in the Kesikköprü Iron Deposit. Available online: https://www.ozcemaden.com/demir-cevheri-uretimi (accessed on 8 April 2025).
Güngör, K. Production of Heavy-Media-Quality Magnetite Concentrate from Kesikköprü Iron Ore Tailings. Master’s Thesis, Middle East Technical University, Ankara, Türkiye, 2010. [Google Scholar]
Ünlü, T. Türkiye Demir Yatakları Arama Çalışmalarında 1. Derecede Ağırlıklı Hedef Saha Seçimi ve Maden Jeolojisi Araştırmaları ile İlgili Proje Teklifi; Report No: 8593; MTA Publication: Ankara, Türkiye, 1989. (In Turkish) [Google Scholar]
Işık, V. The ductile shear zone in granitoid of the Central Anatolian Crystalline Complex, Turkey: Implications for the origins of the Tuzgölü basin during the Late Cretaceous extensional deformation. J. Asian Earth Sci. 2009, 34, 507–521. [Google Scholar] [CrossRef]
Lefebvre, C.; Meijers, M.J.M.; Kaymakci, N.; Peynircioğlu, A.; Langereis, C.G.; Van Hinsbergen, D.J.J. Reconstructing the geometry of central Anatolia during the late Cretaceous: Large-scale Cenozoic rotations and deformation between the Pontides and Taurides. Earth Planet. Sci. Lett. 2013, 366, 83–98. [Google Scholar] [CrossRef]
Seymen, İ. Stratigraphy and metamorphism of the Kırşehir Massif around Kaman (Kırşehir-Turkey). Bull. Geol. Soc. Turk. 1981, 24, 7–14. [Google Scholar]
Bayhan, H. Kesikköprü skarn kuşağının (Bala-Ankara) mineralojisi ve petrojenezi. Hacettepe Üniversitesi Yerbilimleri 1984, 11, 45–59. (In Turkish) [Google Scholar]
Bayhan, H. Geochemistry and genetic interpretation of the Çelebi Instrusion in the Inner Anatolian Granitoid Belt. Geol. Eng. 1986, 29, 27–36, (In Turkish with English abstract). [Google Scholar]
Bayhan, H. Kesikköprü (Bala-Ankara) yöresindeki Fe, Pb-Zn ve florit cevherleşmelerinin mineralojisi. Cumhuriyet Üniversitesi Mühendislik Fakültesi Dergisi 1990, 6–7, 25–33. (In Turkish) [Google Scholar]
Doğan, B.; Ünlü, T.; Sayılı, S. An approach to the origin of Kesikköprü (Bala-Ankara) iron deposit. Bull. Miner. Res. 1998, 120, 1–35. [Google Scholar]
Kuşcu, İ. Potential of porphyry Cu mineralization in central Anatolia. Mining Turkey Magazine, October 2014; 38–41. [Google Scholar]
Kuşcu, İ. Geochemistry and mineralogy of the skarns in the Çelebi District, Kırıkkale, Turkey. Turk. J. Earth Sci. 2001, 10, 121–132. [Google Scholar]
Kuşcu, İ.; Tosdal, R.M.; Gencalioğlu-Kuşcu, G.; Friedman, R.; Ullrich, T.D. Late Cretaceous to Middle Eocene magmatism and metallogeny of a portion of the southeastern Anatolian orogenic belt, east-central Turkey. Econ. Geol. 2013, 108, 641–666. [Google Scholar] [CrossRef]
Zeck, H.P.; Ünlü, T. Murmano plütonu’nun yaşı ve ofiyolitle olan ilişkisi (Divriği-Sivas). MTA Derg. 1988, 108, 82–97. [Google Scholar]
Yılmazer, E.; Kuşcu, İ.; Demirela, G. A-B-Kafa Mineralizations in Divriği: Alteration zoning and zoning. Geol. Bull. Turk. 2003, 46, 17–34. [Google Scholar]
Boztuğ, D.; Harlavan, Y. K–Ar ages of granitoids unravel the stages of Neo-Tethyan convergence in the eastern Pontides and central Anatolia, Turkey. Int. J. Earth Sci. 2008, 97, 585–599. [Google Scholar] [CrossRef]
Marschik, R.; Spikings, R.; Kuşcu, İ. Geochronology and stable isotope signature of alteration related to hydrothermal magnetite ores in central Anatolia, Turkey. Miner. Depos. 2008, 43, 111–124. [Google Scholar] [CrossRef]
Öztürk, H.; Kasapçı, C.; Cansu, Z.; Hanilçi, N. Geochemical characteristics of iron ore deposits in central eastern Turkey: An approach to their genesis. Int. Geol. Rev. 2016, 58, 1673–1690. [Google Scholar] [CrossRef]
Kuşcu, İ.; Yılmazer, E.; Güleç, N.; Bayır, S.; Demirela, G.; Gençalioğlu Kuşcu, G.; Kuru, G.S.; Kaymakçı, N. U-Pb and 40Ar-39Ar Geochronology and isotopic constraints on the genesis of copper-gold−bearing iron oxide deposits in the Hasançelebi district, Eastern Turkey. Econ. Geol. 2011, 106, 261–288. [Google Scholar] [CrossRef]
Boroviczeny, F. 200/240 Nolu Ruhsat Sahasinin Kesikköprü Yakinindaki Demir Yataği Hakkindaki Rapor; Report No: 3481; MTA Publication: Ankara, Türkiye, 1964. (In Turkish) [Google Scholar]
Brennich, G. Çelebi-Kesikköprü-Hirfanli Bölgesinde Manyetit Zuhurlari Hakkinda Rapor; Report No: 2755; MTA Publication: Ankara, Türkiye, 1960. (In Turkish) [Google Scholar]
Demiröz, T.; Ceylan, Ü.; Okşaş, M. Kesikköprü-Bala-Ankara Madentepe Büyükocak Boyali in Demir Yataklari Fizibilite Etüdü; Report No: 8286; MTA Publication: Ankara, Türkiye, 1986. (In Turkish) [Google Scholar]
İşbaşarır, O.; Arda, N.; Tosun, S. Kesikköprü (Bala-Ankara) Demir Yatağı Maden Geçidi, Suluocak ve Boyalı in Ocağı Detay Jeoloji ve Jeofizik Raporu; Report No: 10649; MTA Publication: Ankara, Türkiye, 2004. (In Turkish) [Google Scholar]
Öztürk, K.; Kurt, M.; Öztürk, M.; Sarı, İ. Ankara–Bala–Kesikköprü, Madentepe, Büyükocak, Çataldere, Camiisagir Demir Yatakları Jeoloji ve Rezerv Raporu; Report No: 7355; MTA Publication: Ankara, Türkiye, 1983. (In Turkish) [Google Scholar]
Öztürk, K.; Öztürk, M. Ankara-Bala-Yukarıtepeköy-Kartalkaya Demir Cevherleşmesi Jeoloji Etüd ve Arama Raporu; Report No: 7357; MTA Publication: Ankara, Türkiye, 1983. (In Turkish) [Google Scholar]
Öztürk, M. Ankara-Keskin-Çelebi, Kırşehir-Kaman, Nevşehir-Hacıbektaş Yörelerindeki Demir Zuhurlarının Jeoloji Raporu; Report No: 7158; MTA Publication: Ankara, Türkiye, 1981. (In Turkish) [Google Scholar]
Sözen, A. Kesikköprü, Madentepe Manyetit Zuhur Hakkinda Rapor; Report No: 4212; MTA Publication: Ankara, Türkiye, 1970. (In Turkish) [Google Scholar]
Sungurlu, B. Kesikköprü-Çelebi-Hirfanli Bölgesinin Manyetit Zuhurlari Hakkinda Rapor; Report No: 4231; MTA Publication: Ankara, Türkiye, 1970. (In Turkish) [Google Scholar]
Yaz, N.; Sözen, A. Kesikköprü-Çelebi-Hirfanli Bölgesinin Manyetit + Hematit Zuhurlari Hakkinda Rapor; Report No: 4440; MTA Publication: Ankara, Türkiye, 1967. (In Turkish) [Google Scholar]
Wondenmagegnahu, T.W. Mineralogy, Chemistry and Physical Properties of the Magnetite Ore Deposits Around Kesikköprü Village and the Surrounding Areas. Master’s Thesis, Middle East Technical University, Ankara, Türkiye, 1990. [Google Scholar]
Robertson, A.H.F.; Dixon, J.E. Introduction: Aspects of the Geological Evolution of the Eastern Mediterranean. Geol. Soc. Lond. Spec. Publ. 1984, 17, 1–74. [Google Scholar] [CrossRef]
Şengör, A.M.C.; Yilmaz, Y. Tethyan evolution of Turkey: A plate tectonic approach. Tectonophysics 1981, 75, 181–241. [Google Scholar] [CrossRef]
Görür, N.; Tüysüz, O.; Sengör, A.M.C. Tectonic evolution of the Central Anatolian Basins. Int. Geol. Rev. 1998, 40, 831–850. [Google Scholar] [CrossRef]
Akıman, O.; Erler, A.; Göncüoğlu, M.C.; Güleç, N.; Geven, A.; Türeli, T.K.; Kadıoğlu, Y.K. Geochemical characteristics of granitoids along the western margin of the Central Anatolian Crystalline Complex and their tectonic implications. Geol. J. 1993, 28, 371–382. [Google Scholar] [CrossRef]
Erkan, Y.; Ataman, G. A study on the age of metamorphism of central Anatolian massive (Kırşehir region) by K-Ar method. Yerbilimleri 1981, 8, 27–30. [Google Scholar]
Göncüoğlu, M.C. Geochronological data from the southern part (Niğde area) of the Central Anatolian Massif. Miner. Res. Tech. Inst. Turk. Bull. 1986, 105–106, 83–96. [Google Scholar]
Whitney, D.L.; Hamilton, M.A. Timing of high-grade metamorphism in central Turkey and the assembly of Anatolia. J. Geol. Soc. 2004, 161, 823–828. [Google Scholar] [CrossRef]
Alpaslan, M.; Guzeou, J.C.; Bonhomme, M.; Boztuğ, D. Metamorphism and age of the Fındıcak metamorphics of Yıldızeli metasedimentary group. Geol. Bull. Turk. 1996, 39, 19–29. [Google Scholar]
Whitney, D.L.; Teyssier, C.; Fayon, A.K.; Hamilton, M.A.; Heizler, M. Tectonic controls on metamorphism, partial melting, and intrusion: Timing and duration of regional metamorphism and magmatism in the Niğde Massif, Turkey. Tectonophysics 2003, 376, 37–60. [Google Scholar] [CrossRef]
Whitney, D.L.; Teyssier, C.; Heizler, M.T. Gneiss domes, metamorphic core complexes, and wrench zones: Thermal and structural evolution of the Niğde Massif, central Anatolia. Tectonics 2007, 26, TC5002. [Google Scholar] [CrossRef]
Yalınız, M.K.; Floyd, P.A.; Göncüoğlu, M.C. Supra-subduction zone ophiolites of Central Anatolia: Geochemical evidence from the Sarikaraman Ophiolite, Aksaray, Turkey. Mineral. Mag. 1996, 60, 697–710. [Google Scholar] [CrossRef]
Göncüoğlu, M.C.; Türeli, T.K. Petrology and geodynamic interpretation of plagiogranites from Central Anatolian Ophiolites (Aksaray-Turkey). Turk. J. Earth Sci. 1993, 2, 195–203. [Google Scholar]
Yılmaz, S.; Boztuğ, D. Petrology of the Hasançelebi Syenitic Pluton from the Central-Eastern Anatolian Alkaline Province, Hekimhan-Malatya District, Turkey. In Proceedings of the EUG VI, Strasbourg, France, 1–4 March 1991; p. 246. [Google Scholar]
Otlu, N.; Boztuğ, D. The coexistency of the silica oversaturated (ALKOS) and undersaturated alkaline (ALKUS) rocks in the Kortundağ and Baranadağ plutons from the Central Anatolian alkaline plutonism, E Kaman/NW Kırşehir, Turkey. Turk. J. Earth Sci. 1998, 7, 241–258. [Google Scholar]
Erler, A.; Bayhan, H. General evalution and problems of the central Anatolian granitoids. Yerbilimleri. 1995, 17, 49–69. [Google Scholar]
Erler, A.; Akiman, O.; Unan, C.; Dalkilic, F.; Dalkilic, Β.; Geven, A.; Önen, P. Petrology and geochemistry of the magmatic rocks of the Kirsehir Massif at Kaman (Kirsehir) and Yozgat regions. TÜBİTAK Doğa-Tr. J. Eng. Environ. Sci. 1991, 15, 76–100. [Google Scholar]
Erler, A.; Göncüoğlu, M.C. Geologic and tectonic setting of the Yozgat Batholith, Northern Central Anatolian Crystalline Complex, Turkey. Int. Geol. Rev. 1996, 38, 714–726. [Google Scholar] [CrossRef]
Köksal, S.; Romer, R.L.; Göncüoğlu, M.C.; Toksoy-Köksal, F. Timing of post-collision H-type to A-type granitic magmatism: U–Pb titanite ages from the Alpine central Anatolian granitoids (Turkey). Int. J. Earth Sci. 2004, 93, 974–989. [Google Scholar] [CrossRef]
Ataman, G. Ankara’nın güneydoğusundaki granitik-granodiyoritik kütlelerden Cefalıkdağın radyometrik yaşı hakkında ön çalışma. Hacet. Üniversitesi Fen Ve Mühendislik Bilim. Dergisi 1972, 2, 44–49. [Google Scholar]
Ayan, M. Contribution a L’etude Petrografhique et Geologique de la Region Situee an North-East de Kaman; No: 15; MTA Publication: Ankara, Türkiye, 1963. [Google Scholar]
Boztuğ, D.; Tichomirowa, M.; Bombach, K. ²⁰⁷Pb-²⁰⁶Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous godynamic evolution of the central Anatolian crust, Turkey. J. Asian Earth Sci. 2007, 31, 71–86. [Google Scholar] [CrossRef]
Boztuğ, D.; Jonckheere, R.C.; Heizler, M.; Ratschbacher, L.; Harlavan, Y.; Tichomirova, M. Timing of post-obduction granitoids from intrusion through cooling to exhumation in central Anatolia, Turkey. Tectonophysics 2009, 473, 223–233. [Google Scholar] [CrossRef]
Güleç, N. Rb-Sr isotope data from the Ağaçören granitoid (East of Tuz Gölü), geochronological and genetical implications. Turk. J. Earth Sci. 1994, 3, 39–43. [Google Scholar]
Gündoğdu, M.N.; Bros, R.; Kuruç, A.; Bayhan, H. Rb–Sr whole rock systematics of the Bayındır (Kaman-Kırşehir) feldspathoidal syenites. In Proceedings of the Hacettepe University 20th Anniversary of Earth Sciences Symposium, Ankara, Türkiye, 25–27 October 1988; p. 55. [Google Scholar]
Isik, V.; Lo, C.H.; Göncüoğlu, C.; Demirel, S. ³⁹Ar/⁴⁰Ar ages from the Yozgat Batholith: Preliminary data on the timing of Late Cretaceous extension in the Central Anatolian Crystalline Complex, Turkey. J. Geol. 2008, 116, 510–526. [Google Scholar] [CrossRef]
İlbeyli, N.; Pearce, J.A.; Thirwall, M.F.; Mitchell, J.G. Petrogenesis of collision-related plutonics in central Anatolia, Turkey. Lithos 2004, 72, 163–182. [Google Scholar] [CrossRef]
Kadioglu, Y.K.; Dilek, Y.; Güleç, N.; Foland, K.A. Tectonomagmatic evolution of bimodal plutons in the Central Anatolian Crystalline Complex, Turkey. J. Geol. 2003, 111, 671–690. [Google Scholar] [CrossRef]
Kadıoglu, Y.K.; Dilek, Y.; Foland, K.A. Slab break-off and syncollisional origin of the Late Cretaceous magmatism in the Central Anatolian crystalline complex. In Postcollisional Tectonics and Magmatism in the Mediterranean Region and Asia; Dilek, Y., Pavlides, S., Eds.; Special Paper; Geological Society of America: Boulder, CO, USA, 2006; Volume 409, pp. 381–415. [Google Scholar] [CrossRef]
Kalkancı, Ş. Etude Géologique et Pétrochimique du Sud de le Region de Suşehri. Géochronologie du Massif Syenitque de Kösedağ (NE de Sivas-Turquie). Ph.D. Thesis, L’Univérsite de Grenoble, Saint-Martin-d’Hères, France, 1974. [Google Scholar]
Köksal, S.; Möller, A.; Göncüoglu, M.C.; Frei, D.; Gerdes, A. Crustal homogenization revealed by U–Pb zircon ages and Hf isotope evidence from the Late Cretaceous granitoids of the Agaçören intrusive suite (Central Anatolia/Turkey). Contrib. Mineral. Petrol. 2012, 163, 725–743. [Google Scholar] [CrossRef]
Kuruç, A. Rb–Sr Geochemistry of Syenitoids from Kaman–Kırşehir Region. Master’s Thesis, Hacettepe University, Ankara, Türkiye, 1990. [Google Scholar]
Tatar, S.; Boztuǧ, D. The syn-collisional Danacıobası biotite leucogranite derived from the crustal thickening in central Anatolia (Kırıkkale), Turkey. Geol. J. 2005, 40, 571–591. [Google Scholar] [CrossRef]
Terzi, M.H. The Mineralogy, Petrography and Geochemistry of Kesikköprü Fe-Oxide Deposit, Bala-Ankara. Master’s Thesis, Aksaray University, Aksaray, Türkiye, 2014. [Google Scholar]
Zeck, H.P.; Ünlü, T. Parallel whole rock isochrons from a composite, monzonitic pluton, Alpine belt, Central Anatolia, Turkey. Neues Jahrbuch für Mineralogie Monatshefte 1987, 5, 193–204. [Google Scholar]
Göncüoğlu, M.C.; Toprak, V.; Kuşcu, İ.; Erler, A.; Olgun, E.; Rojay, B. Orta Anadolu Masifinin Batı Bölümünün Jeolojisi, Bölüm 2: Orta Kesim; Report No: 3155; TPAO publication: Ankara, Türkiye, 1992. (In Turkish) [Google Scholar]
Göncüoğlu, M.C.; Erler, A.; Toprak, V.; Olgun, E.; Yalınız, K.; Kuşcu, İ.; Köksal, S.; Dirik, K. Orta Anadolu Masifinin Orta Bölümünün Jeolojisi, Bölüm 3: Orta Kızılırmak Tersiyer Baseni’nin Jeolojik Evrimi; Report No: 3313; TPAO publication: Ankara, Türkiye, 1993. (In Turkish) [Google Scholar]
Akçay, A.E.; Dönmez, M.; Kara, H.; Yergök, A.F.; Esentürk, K. 1:100.000 Ölçekli Türkiye Jeoloji Haritaları: Kırşehir-J30 Paftası; No: 91; MTA Publication: Ankara, Türkiye, 2008. (In Turkish) [Google Scholar]
Bailey, E.B.; Mc Callien, W.J. Ankara melanjı ve Anadolu şariyajı. Bull. Min. Res. Exp. 1950, 40, 17–21. (In Turkish) [Google Scholar]
Kuşcu, İ.; Gençalioğlu Kuşcu, G.; Meinert, L.D.; Floyd, P.A. Tectonic setting and petrogenesis of the Çelebi granitoid (Kırıkkale-Turkey) and comparasion with world skarn granitoids. J. Geochem. Exp. 2002, 76, 175–194. [Google Scholar] [CrossRef]
Orhan, A. Mineralogy, fluid inclusions and carbon isotopes of the Kaman iron deposits, Central Anatolia, Turkey: Implication for ore genesis and hydrothermal evolution. Ore Geol. Rev. 2020, 127, 103808. [Google Scholar] [CrossRef]
Kuşcu, İ.; Gençalioğlu Kuşcu, G.; Sarac, C.; Meinert, L.D. An approach to geochemical characterization of productive versus barren granitoids in terms of iron in Central Turkey. J. Asian Earth Sci. 2004, 24, 311–325. [Google Scholar] [CrossRef]
Vefa Mineral Mining Incorporation. Operation and assessment report of the Bugüz iron ore. Kırşehir, Türkiye, 2018; Unpublished Technical Report. [Google Scholar]
Mercan, M.; Tiringa, D.; Canıgür, C.; Taştan, M. Ankara-Bala-Kesikköprü demir sahası yeni bulgular. MTA Doğal Kay. Ekon. Bült. 2020, 29, 125–129. (In Turkish) [Google Scholar]
Staudacher, T.; Jessberger, E.K.; Dorflinger, D.; Kiko, J. A refined ultrahigh-vacuum furnace for rare gas analysis. J. Phys. E Sci. Instrum. 1978, 11, 781. [Google Scholar] [CrossRef]
Lee, J.Y.; Marti, K.; Severinghaus, J.P.; Kawamura, K.; Yoo, H.S.; Lee, J.B.; Kim, J.S. A redetermination of the isotopic abundances of atmospheric Ar. Geochim. Cosmochim. Acta 2006, 70, 4507–4512. [Google Scholar] [CrossRef]
Koppers, A.A. ArArCALC-software for ⁴⁰Ar/³⁹Ar age calculations. Comp. Geosci. 2002, 28, 605–619. [Google Scholar] [CrossRef]
Renne, P.R.; Swisher, C.C.; Deino, A.L.; Karner, D.B.; Owens, T.L.; DePaolo, D.J. Intercalibration of standards, absolute ages and uncertainties in ⁴⁰Ar/³⁹Ar dating. Chem. Geol. 1998, 145, 117–152. [Google Scholar] [CrossRef]
Min, K.; Mundil, R.; Renne, P.R.; Ludwig, K.R. A test for systematic errors in ⁴⁰Ar/³⁹Ar geochronology through comparison with U/Pb analysis of a 1.1-Ga rhyolite. Geochim. Cosmochim. Acta 2000, 64, 73–98. [Google Scholar] [CrossRef]
Clayton, R.N.; Mayeda, T.K. The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis. Geochim. Cosmochim. Acta 1963, 27, 43–52. [Google Scholar] [CrossRef]
Shand, S.J. Eruptive Rocks: Their Genesis, Composition, Classification, and Their Relation to Ore-Deposits with a Chapter on Meteorite; John Wiley & Sons: New York, NY, USA, 1943. [Google Scholar]
Güllü, B.; Akşit, A. Fingerprint of magma mixture in the leucogranites: Spectroscopic and petrochemical approach, Kalebalta-Central Anatolia, Türkiye. Open Geosci. 2023, 15, 20220548. [Google Scholar] [CrossRef]
Pearce, J.A.; Harris, N.B.W.; Tindle, A.G. Trace-element discrimation diagrams for the tectonic interpretation of granitic rocks. J. Petrol. 1984, 25, 956–983. [Google Scholar] [CrossRef]
Pearce, J.A. Sources and settings of granitic rocks. Episodes 1996, 19, 120–125. [Google Scholar] [CrossRef]
Batchelor, R.A.; Bowden, P. Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chem. Geol. 1985, 48, 43–55. [Google Scholar] [CrossRef]
Harris, N.B.W.; Pearce, J.A.; Tindle, A.G. Geochemical characteristics of collision-zone magmatism. Geol. Soc. Lond. Spec. Publ. 1986, 19, 67–81. [Google Scholar] [CrossRef]
Cox, K.G.; Bell, J.D.; Pankhurst, R.J. The Interpretation of Igneous Rocks; George Allen and Unwin: London, UK, 1979; p. 450. [Google Scholar]
Irvine, T.N.; Baragar, W.R.A. A guide to the chemical classification of the common volcanic rocks. Can. J. Earth Sci. 1971, 8, 523–548. [Google Scholar] [CrossRef]
Peccerillo, A.; Taylor, S.R. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contrib. Mineral. Petrol. 1976, 58, 63–81. [Google Scholar] [CrossRef]
Pearce, J.A. Role of subcontinental lithosphere in magma genesis at active continental margins. In Continental Basalts and Mantle Xenoliths; Hawkesworth, C.J., Norry, M.J., Eds.; Shiva Publishing: Nantwich, Cheshire, UK, 1983; pp. 230–249. [Google Scholar]
Boynton, W.V. Cosmochemistry of the rare earth elements: Meteorite studies. In Developments in Geochemistry; Elsevier: Amsterdam, The Netherlands, 1984; Volume 2, pp. 63–114. [Google Scholar] [CrossRef]
Christiansen, E.H.; Keith, J.D. Trace element systematics in silicic magmas: A metallogenic perspective. In Trace Element Geochemistry of Volcanic Rocks: Applications for Massive Sulfide Exploration; Wyman, D.A., Ed.; Short Course Notes; Geological Association of Canada: St. John’s, NL, Canada, 1996; Volume 12, pp. 115–151. [Google Scholar]
Brooks, C.; Hart, S.R.; Wendt, I. Realistic use of two-error regression treatments as appliedto rubidium-strontium data. Rev. Geophy. 1972, 10, 551–577. [Google Scholar] [CrossRef]
Dilek, Y.; Thy, P. Age and petrogenesis of plagiogranite intrusions in the Ankara mélange, central Turkey. Isl. Arc 2006, 15, 44–57. [Google Scholar] [CrossRef]
Rollinson, H. Using Geochemical Data; Longman Scientific and Technical: Essex, UK, 1993; p. 352. [Google Scholar]
Zindler, A.; Hart, S. Chemical geodynamics. Annu. Rev. Earth Planet. Sci. 1986, 14, 493–571. [Google Scholar] [CrossRef]
Faure, G. Principles of Isotope Geology, 2nd ed.; Wiley: New York, NY, USA, 1986. [Google Scholar]
Meinert, L.D.; Hedenquist, J.W.; Satoh, H.; Matsuhisa, Y. Formation of anhydrous and hydrous skarn in Cu-Au ore deposits by magmatic fluids. Econ. Geol. 2003, 98, 147–156. [Google Scholar] [CrossRef]
Orhan, A.; Mutlu, H.; Fallick, A.E. Fluid infiltration effects on stable isotope systematics of the Susurluk skarn deposit, NW Turkey. J. Asian Earth Sci. 2011, 40, 550–568. [Google Scholar] [CrossRef]
Oyman, T.; Özgenç, İ.; Tokcaer, M.; Akbulut, M. Petrology, geochemistry, and evolution of the iron skarns along the northern contact of the Eğrigöz Plutonic Complex, Western Anatolia, Turkey. Turk. J. Earth Sci. 2013, 22, 61–97. [Google Scholar] [CrossRef]
Oyman, T. Geochemistry, mineralogy and genesis of the Ayazmant Fe–Cu skarn deposit in Ayvalık, (Balikesir), Turkey. Ore Geol. Rev. 2010, 37, 175–201. [Google Scholar] [CrossRef]
Ozturk, Y.Y.; Helvaci, C. Skarn alteration and Au-Cu mineralization associated with Tertiary granitoids in northwestern Turkey: Evidence from the Evciler deposit, Kazdag Massif, Turkey. Econ. Geol. 2008, 103, 1665–1682. [Google Scholar] [CrossRef]
Sipahi, F.; Akpınar, İ.; Eker, Ç.S.; Kaygusuz, A.; Vural, A.; Yılmaz, M. Formation of the Eğrikar (Gümüşhane) Fe–Cu skarn type mineralization in NE Turkey: U–Pb zircon age, lithogeochemistry, mineral chemistry, fluid inclusion, and O-H-C-S isotopic compositions. J. Geochem. Exp. 2017, 182, 32–52. [Google Scholar] [CrossRef]
Yılmazer, E.; Güleç, N.; Kuşcu, İ.; Lentz, D.R. Geology, geochemistry, and geochronology of Fe-oxide Cu (±Au) mineralization associated with Şamlı pluton, western Turkey. Ore Geol. Rev. 2014, 57, 191–215. [Google Scholar] [CrossRef]
Demir, Y.; Uysal, İ.; Kandemir, R.; Jauss, A. Geochemistry, fluid inclusion and stable isotope constraints (C and O) of the Sivrikaya Fe-skarn mineralization (Rize, NE Turkey). Ore Geol. Rev. 2017, 91, 153–172. [Google Scholar] [CrossRef]
Coleman, M.L. Sulphur isotopes in petrology. J. Geol. Soc. 1977, 133, 593–608. [Google Scholar] [CrossRef]
Zheng, Y.F. Calculation of oxygen isotope fractionation in anhydrous silicate minerals. Geochim. Cosmochim. Acta 1993, 57, 1079–1091. [Google Scholar] [CrossRef]
Zheng, Y.F. Calculation of oxygen isotope fractionation in hydroxyl-bearing silicates. Earth Planet. Sci. Lett. 1993, 120, 247–263. [Google Scholar] [CrossRef]
Zheng, Y.F. Oxygen isotope fractionation in magnetites: Structural effect and oxygen inheritance. Chem. Geol. 1995, 121, 309–316. [Google Scholar] [CrossRef]
Zheng, Y.F. Oxygen isotope fractionation in carbonate and sulfate minerals. Geochem. J. 1999, 33, 109–126. [Google Scholar] [CrossRef]
Suzuoki, T.; Epstein, S. Hydrogen isotope fractionation between OH-bearing minerals and water. Geochim. Cosmochim. Acta 1976, 40, 1229–1240. [Google Scholar] [CrossRef]
Graham, C.M.; Sheppard, S.M.; Heaton, T.H. Experimental hydrogen isotope studies-I. systematics of hydrogen isotope fractionation in the systems epidote-H₂O, zoisite-H₂O and AlO(OH)-H₂O. Geochim. Cosmochim. Acta 1980, 44, 353–364. [Google Scholar] [CrossRef]
Epstein, S.; Sharp, R.P.; Gow, J. Six-year record of hydrogen and oxygen isotope variations in South Pole firn. J. Geophys. Res. 1965, 70, 1809–1814. [Google Scholar] [CrossRef]
Epstein, S.; Sharp, R.P.; Gow, J. Antarctic ice sheet: Stable isotope analysis of Byrd Station cores and interhemispheric climatic implications. Science 1970, 168, 1570–1572. [Google Scholar] [CrossRef]
Sheppard, S.M.F. The Cornubian batholiths, SW England: D/H and ¹⁸O/¹⁶O studies of kaolinite and other alteration minerals. J. Geol. Soc. 1977, 133, 573–591. [Google Scholar] [CrossRef]
Sheppard, S.M.F. Stable isotope geochemistry of fluids. Phys. Chem. Earth 1981, 13–14, 419–445. [Google Scholar] [CrossRef]
Taylor, H.P. The application of oxygen and hydrogen isotope studies to problems of hydrothermal alteration and ore deposition. Econ. Geol. 1974, 69, 843–883. [Google Scholar] [CrossRef]
Gençalioğlu-Kuşcu, G.; Göncüoğlu, M.C.; Kuşcu, İ. Post-collisional magmatism on the northern margin of the Taurides and its geological implications: Geology and petrology of the Yahyalı-Karamadazı Granitoid. Turk. J. Earth Sci. 2001, 10, 103–119. [Google Scholar]
Kuşcu, İ. Skarns and skarn deposits of Turkey. In Mineral Resources of Turkey; Modern Approaches in Solid Earth, Sciences; Pirajno, F., Ünlü, T., Dönmez, C., Şahin, M., Eds.; Springer: Cham, Switzerland, 2019; Volume 16, pp. 283–336. [Google Scholar] [CrossRef]
Gürgen, M. A Geological Evaluation of Distinct Intrusion-Related Mineralization Styles at the Çubuklu Prospect (Yahyalı, Central Anatolia). Master’s Thesis, Middle East Technical University, Ankara, Türkiye, 2024. [Google Scholar]
Tükel, F.Ş.; Tiringa, D.; Hanilçi, N.; Ateşçi, B.; Aysal, N.; Alan, İ. Geochemistry and U-Pb dating of the Yahyalı pluton and associated skarn occurrences, SW Kayseri (Central Türkiye): Geodynamic significance and relation to mineralization. J. Geochem. Exp. 2025, 274, 107756. [Google Scholar] [CrossRef]
Delibaş, O. The Role of Magma Mixing Processes in the Formation of Iron, Copper, Molybdenum and Lead Mineralizations of Kırıkkale-Yozgat Region. Ph.D. Thesis, Hacettepe University, Ankara, Türkiye, 2009. [Google Scholar]
Delibaş, O.; Genç, Y.; De Campos, C.P. Magma mixing and unmixing related mineralization in the Karacaali Magmatic Complex, central Anatolia, Turkey. Geol. Soc. Lond. Spec. Publ. 2011, 350, 149–173. [Google Scholar] [CrossRef]
Delibaş, O.; Genc, Y. Re-Os molybdenite ages of granitoid-hosted Mo–Cu occurrences from central Anatolia (Turkey). Ore Geol. Rev. 2012, 44, 39–48. [Google Scholar] [CrossRef]
Ohmoto, H.; Rye, R.O. Isotopes of sulfur and carbon. In Geochemistry of Hydrothermal Ore Deposits; Barnes, H.L., Ed.; Wiley: New York, NY, USA, 1979; pp. 509–567. [Google Scholar]
Gençalioğlu-Kuşcu, G.; Floyd, P.A. Mineral compositional and textural evidence for magma mingling in the Saraykent volcanics. Lithos 2001, 56, 207–230. [Google Scholar] [CrossRef]
Boztuğ, D. S-I-A type intrusive associations: Geodynamic significance of synchronism between metamorphism and magmatism in Central Anatolia, Turkey. Geol. Soc. Lond. Spec. Publ. 2000, 173, 441–485. [Google Scholar] [CrossRef]
Meinert, L.D. Skarns and skarn deposits. Geosci. Can. 1992, 19, 145–162. [Google Scholar]
Bowman, J.R.; Covert, J.J.; Clark, A.H.; Mathieson, G.A. The CanTung E Zone scheelite skarn orebody, Tungsten, Northwest Territories; oxygen, hydrogen, and carbon isotope studies. Econ. Geol. 1985, 80, 1872–1895. [Google Scholar] [CrossRef]
Marcke de Lummen, V.G. Oxygen and hydrogen isotope evidence for influx of magmatic water in the formation of W-Mo-and Sn-bearing skarns in pelitic rocks at Costabonne, France, and Land’s End, England. In Proceedings of the 7th Quadrennial IAGOD Symposium, Stuttgart, Germany, 18–22 August 1988; pp. 355–362. [Google Scholar]
Williams-Jones, A.E.; Heinrich, C.A. Vapor transport of metals and the formation of magmatic-hydrothermal ore deposits. 100th anniversary special paper. Econ. Geol. 2005, 100, 1287–1312. [Google Scholar] [CrossRef]
Ayuso, R.A.; Barton, M.D.; Blakely, R.J.; Bodnar, R.J.; Dilles, J.H.; Graybeal, F.T.; Mars, J.C.; McPhee, D.K.; Seal, R.R.; Taylor, R.D.; et al. Porphyry Copper Deposit, Model; US Geological Survey Scientific Investigations Report (2010-5070-B); US Geological Survey: Reston, VA, USA, 2010; p. 169. [Google Scholar]
Monecke, T.; Monecke, J.; Reynolds, T.J.; Tsuruoka, S.; Bennett, M.M.; Skewes, W.B.; Palin, R.M. Quartz solubility in the H2O-NaCl system: A framework for understanding vein formation in porphyry copper deposits. Econ. Geol. 2018, 113, 1007–1046. [Google Scholar] [CrossRef]
Meinert, L.D.; Brooks, J.W.; Myers, G.L. Whole rock geochemistry and contrast among skarn types. In Geology and Ore Deposits of the Great Basin: Reno, Nevada; Buffa, R.H., Coyner, A.R., Eds.; Fieldtrip Guidebook Compendium; Geological Society of Nevada: Reno, NV, USA, 1991; Volume 1, pp. 72–80. [Google Scholar]
Meinert, L.D.; Dipple, G.M.; Nicolescu, S. World skarn deposits. In 100th Anniversary Volume; Society of Economic Geologists: Littleton, CO, USA, 2005; pp. 299–336. [Google Scholar] [CrossRef]
Warr, L.N. IMA–CNMNC approved mineral symbols. Mineral. Mag. 2021, 85, 291–320. [Google Scholar] [CrossRef]

Figure 4. (a) Magnetite vein in the garnet–pyroxene (±phlogopite ± epidote) subzone; (b) photomicrograph of the disseminated magnetite in the garnet–pyroxene (±phlogopite ± epidote) subzone; (c) banded magnetite within marble; (d) massive magnetite in the epidote subzone; (e) brecciated magnetite with garnet and pyroxene; (f) magnetite replacing the phlogopite; (g) magnetite and its martitisation; (h) fault-controlled hematite- and limonite-rich zone; (i) magnetite replaced by pyrite and chalcopyrite; (j) the photomicrograph of pyrite and chalcopyrite; (k) pyrite (Py) replaced by marcasite (Mrc); (l) malachite and hematite–limonite in the marble.

Figure 5. The paragenetic sequence diagram of gangue and ore minerals in the Kesikköprü iron deposit (thick, thin, and dashed lines refer to major, minor, and trace amounts of minerals, respectively).

Figure 10. ⁴⁰Ar/³⁹Ar plateau age of biotite in granodiorite.

Table 2. Sr and Nd radiogenic isotope composition data.

Sample No	Explanation	Rb	Sr	⁸⁷Sr/⁸⁶Sr	Std. Error *	(⁸⁷Sr/⁸⁶Sr)_i	εSr	(εSr)_i	Sm	Nd	¹⁴³Nd/¹⁴⁴Nd	Std. Error *	(¹⁴³Nd/¹⁴⁴Nd)_i	εNd	(εNd)_i
		ppm	ppm						ppm	ppm
KK-16-01	Magnetite ore	0.40	14.00	0.707964	±25	0.707878	44.89	44.96	0.15	1.00	0.512247	±8	0.512181	−7.63	−7.08
KK-16-02	Exoskarn (Grt ± Px ± Phl)	0.60	6.50	-	±0	-	-	-	0.12	0.80	0.512161	±24	0.512095	−9.30	−8.75
KK-16-03	Endoskarn (Grt − Px ± Phl ± Ep)	2.80	829.00	0.708846	±8	0.708836	57.41	58.56	3.99	20.60	0.512287	±2	0.512202	−6.85	−6.67
KK-16-04	Granitoid	200.70	460.20	0.710242	±10	0.708924	77.21	59.80	3.87	25.00	0.512272	±2	0.512204	−7.14	−6.63
KK-16-05	Mafic–ultramafic	14.20	355.80	0.709416	±7	0.709122	65.49	64.48	1.80	6.10	0.512498	±3	0.512181	−2.73	−4.42
KK-16-06	Exoskarn (Px ± Grt ± Phl ± Ep)	0.90	5.50	-	±0	-	-	-	0.58	2.90	0.512188	±7	0.512100	−8.78	−8.66
KK-16-07	Endoskarn (Grt − Px ± Phl ± Ep)	11.20	193.60	0.709558	±12	0.709383	67.51	66.33	2.88	12.50	0.512288	±3	0.512187	−6.83	−6.97
KK-16-08	Granitoid	195.60	306.30	0.711355	±9	0.709422	93.01	66.88	4.49	26.00	0.512262	±2	0.512186	−7.33	−6.98
2-1	Granitoid	194.00	433.80	0.709607	±3	0.708256	68.20	50.33	4.02	24.80	0.512313	±2	0.512242	−6.34	−5.89
4-2	Granitoid	179.80	445.10	0.709956	±5	0.708735	73.16	57.13	5.43	31.20	0.512291	±2	0.512214	−6.77	−6.42

Abbreviations: Ep: epidote; Grt: garnet; Phl: phlogopite; Px: pyroxene; * standard errors are expressed in the last one or two digits.

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

© 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Share and Cite

MDPI and ACS Style

Yılmazer, E.; Terzi, M.H. Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye). Minerals 2025, 15, 528. https://doi.org/10.3390/min15050528

AMA Style

Yılmazer E, Terzi MH. Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye). Minerals. 2025; 15(5):528. https://doi.org/10.3390/min15050528

Chicago/Turabian Style

Yılmazer, Erkan, and Mustafa Haydar Terzi. 2025. "Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye)" Minerals 15, no. 5: 528. https://doi.org/10.3390/min15050528

APA Style

Yılmazer, E., & Terzi, M. H. (2025). Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye). Minerals, 15(5), 528. https://doi.org/10.3390/min15050528

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Menu

Geochemistry, Isotope Characteristics, and Evolution of the Kesikköprü Iron Deposit (Türkiye)

Abstract

1. Introduction

2. Geological Framework

2.1. Regional Geologic Setting

2.2. Local Geology

3. Alteration

4. Mineralization

5. Materials and Methods

5.1. Geochemistry

5.2. Geochronology

5.3. Radiogenic Isotope Geochemistry

5.4. Stable Isotope Geochemistry

6. Results

6.1. Whole Rock Geochemistry

6.1.1. Host Rock

6.1.2. Skarn

6.2. Ar/Ar Geochronology

6.3. Radiogenic Isotopes

6.4. Stable Isotopes

7. Discussion

7.1. Temporal Relationship Between the Kesikköprü Granitoid and Mineralization, and Constraints on Other Magmatic–Hydrothermal Systems

7.2. Tectonic Setting and Petrogenesis of the Kesikköprü Granitoid

7.3. Physico-Chemical and Isotopic Constraints on the Skarn Formation

8. Conclusions

Supplementary Materials

Author Contributions

Funding

Data Availability Statement

Acknowledgments

Conflicts of Interest

Abbreviations

References

Share and Cite

Article Metrics

Article Access Statistics

Further Information

Guidelines

MDPI Initiatives

Follow MDPI