Re-Os molybdenite ages of granitoid-hosted Mo–Cu occurrences from central Anatolia (Turkey)

Ore Geology Reviews 44 (2012) 39–48

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Re-Os molybdenite ages of granitoid-hosted Mo–Cu occurrences from central Anatolia (Turkey) Okan Delibaş ⁎, Yurdal Genç Department of Geological Engineering, Hacettepe University, 06800 Beytepe, Ankara, Turkey

a r t i c l e

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Article history: Received 22 November 2010 Received in revised form 2 August 2011 Accepted 8 August 2011 Available online 10 August 2011 Keywords: Re–Os dating Central Anatolian granitoids Mo–Cu occurrences Central Anatolia Turkey

a b s t r a c t The Central Anatolian Crystalline Complex (CACC), where many granitoids are emplaced and related ore occurrences/deposits occur, is tectonically located in the Alpine–Himalayan Belt. The CACC hosts numerous ore occurrences/deposits (Cu, Mo, Fe, Pb and Zn) that are spatially associated with granitoids. The calc-alkaline Karacaali, Baliseyh and Başnayayla granitoids that form the northern granitoid belt of the CACC host important Mo–Cu occurrences. In this paper, we document Re–Os isotopic age data in molybdenites to determine the timing of the granitoid-hosted mineralizations in the CACC. The Re content of molybdenite in the Başnayayla is significantly higher (108.9–148.5 ppm) than molybdenites from the Karacaali (16.3–74.8 ppm) and Balışeyh (4.2 ppm). Two molybdenite samples from Karacaali and two samples from Başnayayla occurrences give Re–Os ages ranging from 73.8± 0.4 to 76.2± 0.4 Ma and 77.1± 0.4 to 78.0± 0.4 Ma, respectively. Furthermore, one molybdenite sample from Balışeyh gives a 73.6± 0.4 Ma Re–Os age. These ages are consistent with those of post-collisional granitoids and indicate close relationship between mineralization events and granitic magma differentiation–crystallization processes. The new Re–Os age data obtained from this study show that mineralization events developed earlier (78–77 Ma) in the East (Başnayayla) as compared with the West (76–73 Ma) (Karacaali and Baslışeyh) of central Anatolia. Moreover, one molybdenite sample from Karacaali gives 76.2 Ma, which is very close to the Başnayala ages (78 and 77.1 Ma). According to these data, one possible explanation is that older molybdenite ages in Karacaali and Başnayayla probably represent the mineralization period related to crystallization–differentiation processes. On the other hand, the younger molybdenite age (73.8 Ma) in the Karacaali may represent prolongation of the life of magmatic– hydrothermal processes/cycles and/or the remobilization of molybdenum within the solidified granitic system by the intrusion of the basic magma. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The Central Anatolian Crystalline Complex (CACC), where many granitoids are emplaced and related ore occurrences/deposits occur, is tectonically located within the Alpine–Himalayan Belt (Boztuğ, 1998; Çemen et al., 1999; İlbeyli et al., 2004; Whitney et al., 2001; Yalınız et al., 2000) (Fig. 1). The CACC consists of metamorphic, ophiolitic, sedimentary and magmatic rocks. The most extensive magmatic rocks are granitoids that were emplaced during the Early to Late Cretaceous (Akıman et al., 1993; Aydın et al., 1998; Boztuğ, 1998; Düzgören-Aydın et al., 2001; İbeyli and Pearce, 2005; İlbeyli et al., 2004; Köksal et al., 2004; Otlu and Boztuğ, 1998; Tatar and Boztuğ, 1998; Yalınız et al., 1999). Granitoids in CACC are mainly classified as syn- and post-collisional granitoids (Akıman et al., 1993; Aydın et al., 1998; Boztuğ, 1998;

⁎ Corresponding author at: General Directorate of Mineral Research & Exploration (MTA), Mineral research and exploration department, Üniversiteler Mah. Dumlupınar Bulv. No:139, 06800, Ankara, Turkey. Tel.:+90 5324714786. E-mail addresses: [email protected], [email protected] (O. Delibaş). 0169-1368/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.oregeorev.2011.08.003

Düzgören-Aydın et al., 2001; İbeyli and Pearce, 2005; İlbeyli et al., 2004; Köksal et al., 2004; Otlu and Boztuğ, 1998; Tatar and Boztuğ, 1998; Yalınız et al., 1999). They have two emplacement peaks ranging between 110 and 84 Ma and 82–67 Ma (İlbeyli, 2005), which are identical to the timing of the collision between Pontide magmatic arc and the northern margin of the Touride–Anatolide continental plate and then the postcollisional period following the main collision event (Akıman et al., 1993; Boztuğ, 2000; Boztuğ et al., 2007a,b,cErler and Göncüoğlu, 1996; Göncüoğlu and Türeli, 1993, 1994; Göncüoğlu et al., 1991, 1992; İlbeyli, 2005; Otlu and Boztuğ, 1998; Türeli et al., 1993). As a result of the collision between Pontide magmatic arc and Touride–Anatolide continent, the slab break-off and lithospheric delamination led to extensional post collisional regime and emplacement of the post-collisional granitoids in the CACC (Boztuğ, 2000; Boztuğ et al., 2007a,b,c, 2009; Düzgören-Aydın et al., 2001; Köksal et al., 2001). This collision between Pontide magmatic arc and Touride–Anatolide continent and following post-collisional events resulted in the formation of different types of ore deposits/occurrences related to granitoids in CACC. Ore deposits/occurrences related to granitoids in CACC can be classified into two groups: (1) Skarn- and (2) Vein-type (quartz–

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Fig. 1. Simplified regional geological map of Central Anatolia and location map of Karacaali Magmatic Complex, Balışeyh Granitoid and Başnayayla Granitoid in Central Anatolia. CACC, Central Anatolian Crystalline Complex; KMC, Karacaali Magmatic Complex; Balışeyh Granitoid; BS, Başnayayla Granitoid; BY, CAFZ: Central Anatolian Fault Zone. [Modified after Ketin (1961), Bingöl (1989); granitoids classification modified after Boztuğ (1998)] (1:Delibaş et al., 2011; 2: Boztuğ et al., 2009; 3: İlbeyli et al., 2004, 4: Tatar et al., 2003).

molybdenite, quartz–galena and fluorite–quartz veins) (Erler and Bayhan, 1998). These deposits are genetically related to Late Cretaceous post-collisional granitoids. The northern granitoid belt of the CACC hosts several vein-type Mo–Cu occurrences/deposits. The most important granitoid-hosted Mo–Cu deposits/occurrences, from west to east, are Karacaali (KMC), Balışeyh (BS) and Başnayayla (BY) (Delibaş, 2009; Delibaş and Genç, 2004; Karabalık et al., 1998; Kuşçu, 2002; Kuşçu and Genç, 1999; Sözeri, 2003) (Fig. 1; Table 1). The calc-alkaline Karacaali, Balışeyh and Başnayayla granitoids, the subject of the present study, are typical examples of Late Cretaceous post-collisional granitoids in the CACC. Mineral exploration and mining were conducted in Balışeyh between 1936 and 1940 by the General Directorate of Mineral Research and Exploration of Turkey (MTA) and Eti Mine. The estimated total reserves in 1937 were 6600 tons at a grade of 2.2% MoS2 (MTA, 1965). The Balışeyh mine has been operated by numerous private mining companies after 1937. From this mine, 11,977 tons of ore with 1–1.5% Mo grades were extracted by the Turk Maadin Company in 1984 (Sözeri, 2003) and it was operated at certain times between 1984 and 2010 by numerous companies. The Başnayayla occurrence in Yozgat was discovered by the MTA in 1993 as part of an exploration program that included geochemical explorations and five diamond-core drill sites. In total, 690 m of drillholes were conducted in the area to determine ore potential and reserves (9375 tons of measured + indicated reserves at 0.02% Mo; Kuşçu and Genç, 1999). On the other hand, the existence of nearly 3750 m 3 of ancient iron-ore slag in the Karacaali (North of Yarımca Hill) shows the ancient mining activities. Furthermore, MTA conducted 1825.20 m of drillholes in total for Fe and Mo–Cu mineralization in the area between 1999 and 2001 (the Cu, Mo, Pb, Zn and Fe-oxide contents are b1.4 wt.%, b0.4 wt.%, b0.1 wt.%, b0.2.wt% and 15–60 wt.%, respectively) (İşbaşarır, et al., 2002; Kuşçu, 2002) (Table 2).

The understanding of the evolution of these occurrences/deposits is critically based on the petrogenesis of the host rock granitoids and the exact timing of mineralization. In recent years, several scientific studies have been conducted, especially on the petrogenesis of the CACC granitoids, including studies on radiogenetic isotopic dating using various techniques (see below). However, the precise timing and genetic relations between the granitoids and ore occurrences/ deposits in the CACC have not been clearly constrained up until now. The present study aims to constrain the timing of the Mo–Cu occurrences/deposits and the relationship between ore formation and magmatic activity in the CACC. For this purpose, we have carried out Re–Os dating studies on molybdenites from the Karacaali (Kırıkkale), Balışeyh (Kırıkkale) and Başnayayla (Yozgat) occurrences. Based on the timing of the mineralizations, we aim to discuss the genetic relationships between the granitoids and Mo–Cu mineralization. This is the first study to present Re–Os age data for Central Anatolian molybdenites.

2. Regional geology The Central Anatolian Crystalline Complex (CACC) (Göncüoğlu et al., 1991) is an important segment of the Alpine–Himalayan collision system (Boztuğ, 2000; Çemen et al., 1999; İlbeyli et al., 2004; Whitney et al., 2001; Yalınız et al., 2000). The CACC is located in the center of Turkey and bound by three main structural zones: the Izmir–Ankara–Erzincan Suture Zone to the North, the Tuz Gölü Fault to the west and the Ecemiş Fault to the East (Erler and Bayhan, 1995; Göncüoğlu et al., 1991, 1992, 1993; Yalınız et al., 1999; Fig. 1). The complex consists mainly of sedimentary, ophiolitic, magmatic and metamorphic rocks. Magmatic rocks intrude into both the ophiolitic and metamorphic rock sequences of the complex. They consist

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Table 1 Classification of the Karacaali (KMC), Balışeyh (BS) and Başnayayla (BY) Mo–Cu occurrences basis on of their host rocks, ore types and ore forms. Location

KMC (Kırıkkale)

BS (Kırıkkale)

BY (Yozgat)

Host-rock type

Porphyritic quartz monzonite Quartz monzonite Fine-grained granite Calc-alkaline, I-type

Granodiorite Quartz–monzonite Amphibole–biotite granite Calc-alkaline, I-,S-type

Zircon U–Pb 73.1 ± 2.2 Ma (Karacaali magmatic complex)

No age data

Geotectonic settings

Post-collisional

Alteration types

Carbonation Epidotization Chloritization

Post-collisional Syn-collisional Propylitic Sericitic Potasic

Biotite–granite Microcline granite Andalusite–sillimanite granite Calc-alkaline, S-,I-type K–Ar* 68.0 ± 0.3 Ma Ar–Ar* 78.1 ± 0.2 Ma 80.0 ± 0.2 Ma (Composite Yozgat Batholith) Post-collisional Syn-collisional Phyllic (quartz–sericite–pyrite) Potassic (quartz–feldspar–biotite) Potassic-phyllic (quartz–feldspar–biotite–sericite)

Silisification Actinolitization N–S orientated vertical/sub-vertical veins (quartz, quartz-carbonate, quartz-tourmaline) Dissemination

E–W orientated subvertivcal veins (pegmatitic quartz, quartz) Dissemination

Geochemical classifications of host-rock Host-rock ages

Orebody form

Ore minerals

Mineralization age

References

Chalcopyrite Molybdenite Galena Sphalerite Pyrite Magnetite ± Covelline ± Bornite Re–Os 76.2–73.8(± 0.4)Ma [This study] Delibaş and Genç, 2004 Delibaş, 2009 Delibaş et al., 2011

Molybdenite Magnetite Pyrite Covelline Wolframite Scheelite ± Powellite ± Ferrimolybdenite Re–Os 73.6 (± 0.4)Ma [This study] Oelsner, 1936 Ladame, 1937 Maucher, 1937 Sözeri, 2003

essentially of granitoids and range in composition from monzodiorite through monzonite to granite and syenite. The late to early Cretaceous age of CACM granitoids has been well established with geochronological data in the region. Ataman (1972) reported Rb–Sr whole rock isochron age of 71 ± 1 Ma for Cefalikdag granitoids. Göncüoğlu (1986) also reported mineral ages (Rb–Sr and K–Ar) with small range (75–78 Ma) and Rb–Sr whole rock isochron age of 95 ± 11 Ma for Üçkapılı granitoid (southern part of the CACM). Whole rock isochron age of Ağaçören granitoids (Kaman) was determined by Güleç (1994) as 110 ± 14 Ma. Tatar et al. (2003) reported K–Ar mineral ages of 69.1 ± 1.4 to 71.5 ± 1.5 Ma for S-type granitoids, and 68.8 ± 1.4 to 81.2 ± 3.4 Ma for H-type granitoids in Kaman region (Behrekdağ). K–Ar mineral age of 79 ± 1.7 Ma also was reported by İlbeyli et al. (2004) for Behrekdağ. İlbeyli et al. (2004) also determined the ages of Cefalikdag quartz monzonite and

Table 2 Reserves and grades of the Karacaali (KMC), Balışeyh (BS) and Başnayayla (BY) Mo-Cu occurrences. Occurrences/ deposits Name BS (Kırıkkale)

Reserves (tons)

6600 (operated in 1937)* 11,977 (operated in 1984)** BY (Yozgat) 9375 (measured + indicated)**** KMC (Kırıkkale) N.A. References

Grades (%) 2.2 MoS2* 1–1.5 Mo** 0.02 Mo*** b0.4 Mo****

*MTA, 1965; **Sözeri, 2003; ***Kuşçu and Genç, 1999; ****Kuşçu, 2002

NW–SE orientated vertical/sub-vertical veins (quartz) Veinlets (quartz) Stockwork Dissemination Chalcopyrite Molybdenite Pyrite Magnetite ± Cubanite ± Pyrrhotite ± Sphalerite ± Galena Re-Os 78.0–77.1 (± 0.4) Ma [This study] Kuşçu and Genç, 1999 *Boztuğ et al., 2009

Baranadağ monzonite as 66.6 ± 1.1 Ma and 76.4 ± 1.3 Ma by mineral K–Ar method. Köksal et al. (2004) reported 74 ± 2.8 Ma age for Htype Baranadağ quartz monzonite and 74.1 ± 0.7 Ma U–Pb titanite age for A-type Çamsarı quartz syenite. Kadıoğlu et al. (2006) obtained 77.7 ± 0.3 Ma age for the granite (e.g. Ağaçören, Behrekdağ, Sulakyurt), 70.0 ± 1.0 Ma age for the monzonite (e.g. Terlemez, Baranadağ, Murmano), and 69.8 ± 0.3 Ma 40Ar– 39Ar ages for the syenite supersuite rocks (e.g., İdişdağ, Bayındır, Akçakent) in Central Anatolia. In addition, Boztuğ et al. (2009) presented 207Pb– 206Pb single zircon evaporation ages, which yield an emplacement age of 95.7 ± 5.1 Ma for the Çamsarı quartz syenite, 75.0 ± 11.0 Ma age for the Hamit quartz syenite and 74.1 ± 4.9 Ma age for the Baranadağ quartz monzonite. Amphibole 40Ar– 39Ar ages reveal a cooling age of ca. 73 Ma for both of the Hamit and Baranadağ units. Furthermore, Delibaş (2009) presented the conventional U–Pb zircon age of 73.1 ± 2.2 Ma for the Karacaali Magmatic Complex monzonitic rocks. The late to early Cretaceous intrusions in the complex were subdivided into genetically four different types; S- (sedimentary), I- (igneous), H- (hybrid); and A- (alkaline). Syn-collisional granitoids are S-type and were formed by the collision of the Pontide magmatic arc with the northern margin of the Touride–Anatolide continental plate (Akıman et al., 1993; Boztuğ et al., 2007a,b,c; Erler and Göncüoğlu, 1996; Göncüoğlu and Türeli, 1993, 1994; Göncüoğlu et al., 1991, 1992; İlbeyli, 2005; Türeli et al., 1993), whereas the post collisional granitoids (I-, H-, and A-type) were generated from magma mixing–mingling processes between mantle material derived from underplating mafic and crustal material derived from felsic magma after the collision event. Underplating mafic magma derived from

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partial melting of upper mantle source rocks by adiabatic decompression under extensional collapse following crustal thickening which resulted from the collision event (Boztuğ, 2000; Otlu and Boztuğ, 1998). After the crustal thickening, lithospheric attenuation caused the decompressional melting of upwelling upper-mantle material to yield within plate alcalic magmatism (A-type) in Central Anatolia (Boztuğ, 2000). 3. Geological settings and Mo–Cu occurrences 3.1. Karacaali Mo–Cu occurrence The Karacaali Mo–Cu occurrence lies within the Karacaali Magmatic Complex (KMC). The KMC is situated within the northwesternmost part of the Central Anatolian granitoid belt (Fig. 1) and consists of volcanic and plutonic rocks (Fig. 2). The volcanic rocks grade from basalt, through andesite, rhyodacite to rhyolite. The calc-alkaline Late Cretaceous (73.1 ± 2.2 Ma Zircon U–Pb age for monzonitic rocks) plutonic rocks

show I-type characteristics and they are composed of gabbro/diorite, monzonite, porphyritic quartz–monzonite, fine-grained granite and porphyritic leucogranite. Oval-shaped, fine-grained and dark graycolored mafic micro-granular enclaves are common in the granitic and monzonitic rocks. Volumetrically, porphyritic quartz-monzonite is the most important rock type in the KMC. Porphyritic quartzmonzonite is characterized by porphyritic texture and it mainly consists of perthitic K-feldspar, plagioclase, quartz, amphibole and biotite. Secondary minerals are calcite, epidote, gypsum and anhydrite. Nearly all lithological units in the KMC have contact with porphyritic quartz-monzonite. The contact of porphyritic quartz-monzonite with the gabbro and basalts is gradational and shows a wide range of hybrid composition. The gabbro/diorite unit crops out as scattered bodies along the contact with porphyritic quartz monzonite. Plagioclase, hornblende, clinopyroxene and magnetite are the essential minerals. Chloritization, sericitization and epidotization are the main alteration processes in the gabbro/ diorite (Delibaş et al., 2011).

Fig. 2. Simplified geological map of the Karacaali Magmatic Complex (KMC) (Delibaş et al., 2011).

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Fig. 3. Vertical distribution of ore vein and samples points for Re-Os chronology within drill holes of Karacaali Mo–Cu occurrence.

In the western part of the complex, a mingling zone between the rhyolites and basalts is observed (Fig. 2). This zone is highly heterogeneous both in mineralogy and texture. In this region, numerous late magmatic veins and dykes crosscut the plutonic rocks. These are quartz-, quartz-tourmaline-, calcite-, quartz-calcite veins and porphyritic leucogranite-, aplite- and basaltic dykes (Delibaş, 2009; Delibaş et al., 2011). The KMC hosts both iron and Mo–Cu occurrences. Iron occurrence is basically hosted by basaltic–andesitic rocks and it mainly consists of magnetite. In addition to these occurrences, porphyritic quartzmonzonite hosts actinolite–magnetite-veins. Mo–Cu in the KMC is related to N–S oriented vertical/sub-vertical quartz-, quartz-carbonate- and quartz–tourmaline veins crosscutting the monzonitic and granitic rocks. Chlorite, actinolite, epidote, calcite and sericite are common alteration products around the veins. On the surface, the vein-type Mo–Cu is not common. It is, therefore, observed in drill core samples. According to drill core (K-1A, K-2, K-3) analysis, the copper, molybdenum, lead and zinc contents are b1.4 wt.%, b0.4 wt.%, b0.1 wt.% and b0.2.wt%, respectively (Kuşçu, 2002). The main opaque minerals are chalcopyrite, molybdenite, galena, sphalerite, pyrite, magnetite, hematite, rutile, covellite and bornite. Limonite, malachite and azurite are also observed in fractures of the monzonitic rocks. Chalcopyrite and molybdenite are usually enriched in quartz veins, whereas sphalerite and galena are commonly observed in carbonate-rich veins. Pyrite, chalcopyrite, sphalerite and magnetite are also found around the veins as impregnations in monzonitic and granitic rocks. Chalcopyrite is more common than pyrite in quartz–calcite veins. Additionally, chalcopyrite inclusions within sphalerite and magnetite are frequent in carbonate- and quartz-rich veins. In the deeper part of the sulfide-rich vein system, magnetite– actinolite veins crosscut the monzonitic rocks. The main ore minerals in the veins are magnetite, hematite and chalcopyrite (; Delibaş, 2009; Delibaş and Genç, 2004; Delibaş et al., 2011) (Fig. 3).

3.2. Balışeyh (BS) Mo–Cu occurrence The post-collisional Balışeyh (BS) granitoid, which hosts Mo–Cu occurrence exposed within the Keskin batholith (Bayhan, 1989; Sözeri,

Fig. 4. Simplified geological map of the Balışeyh Granitoid (BS) (simplified after Sözeri, 2003).

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2003), is situated in nearly 15 km southeast of the Karacaali occurrence (Fig. 1). The Balışeyh granitoid consists of granite, granodiorite, porphyritic granite and gabbro (Sözeri, 2003), (Fig. 4). Granitic rocks are crosscut by quartz-, quartz–pegmatite, pegmatite-veins and aplitic and lamprophyric dykes. Magnetite veins with biotite and pyrite also crosscut granitic rocks (Arni, 1937; MTA, 1965; Oelsner, 1936). The BS granitoid has a calc-alkaline character and exhibits a transition between cafemic and alumino-cafemic associations. Both I- and S-type characteristics have been observed in the granitic and monzonitic rocks of the BS granitoid (Sözeri, 2003). Granodiorite–quartz monzonite and amphibole–biotite granite contain the stockwork and vein-type Mo–Cu mineralization (Ladame, 1937; Sözeri, 2003). Mo–Cu is related to E-W-striking veins. These veins can be classified as pegmatitic quartz veins that are poor in feldspar and quartz veins with biotite. The molybdenite-rich quartz and quartz–pegmatite veins are 30–150 cm in width and 2– 105 m in length (MTA, 1965, 1984; Schumacher, 1937). Veins are commonly brecciated and cut the highly altered monzonitic and granitic rocks. Molybdenite is associated with quartz, but in some cases, it is intergrown with chloritized biotite and magnetite. According to Maucher (1937), quartz-molybdenite veins are younger than magnetite- and pyrite-biotite veins. The main ore minerals of the mineralization are molybdenite, powellite, ferrimolybdenite, magnetite, pyrite, covelline, wolframite and scheelite (Ladame, 1937; Maucher, 1937; MTA, 1965; Oelsner, 1936; Sözeri, 2003). Powellite and ferrimolybdenite with remnants of molybdenite are common in oxidation zones (MTA, 1965).

Three types of alteration observed associated with the mineralization. These are: propylitic, sericitic and potasic alteration zones. Sericitic and potasic alteration zone are observed around the mineralized zones (Sözeri, 2003). The BS Mo–Cu occurrence is described as a brecciated stockwork vein-type molybdenum–copper mineralization and related with potasic alteration zone in the monzonitic and granitic rocks (Sözeri, 2003). 3.3. Başnayayla (BY) Mo–Cu occurrence The Başnayayla granitoid is located within the Yozgat Batholith (Erler and Göncüoğlu, 1996), which is near the northern edge of the Central Anatolian Granitoid belt, approximately 15 km southwest of Yozgat city (Fig. 1). According to Kuşçu and Genç (1999), the Başnayayla granitoid consists mainly of biotite, microcline and andalusite–sillimanite–granite. Felsic and mafic dykes as well as quartz veins crosscut the granitic rocks. Towards the E-SE, gabbroic rocks are also observed (Fig. 5). Tatar and Boztuğ (1998) noted that the Başnayayla gabbro/diorite unit is the youngest magmatic unit of the Şeffatli–Yerköy region. The Başnayayla granitic rocks have both S- and I-type characteristics, but the S-type character is more dominant. Kuşçu and Genç (1999) suggested that the Başnayayla granitic rocks are calc-alkaline, syncollisional intrusions. According to Kuşçu and Genç (1999), biotite granite and andalusite–sillimanite granite contains the disseminated and vein-

Fig. 5. Simplified geological map of the Başnayayla Granitoid (BY) (simplified after Kuşçu and Genç, 1999).

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Fig. 6. Photographs of molybdenite samples taken from Karacaali (a: K2-60; b: K3-39a), Balışeyh (c: BLSH-1), and Başnayayla (d: BM-2-11) occurrences for Re–Os analysis.

type Mo–Cu mineralizations. NW–SE-orientated vertical/sub vertical quartz veins/veinlets cut granitic rocks as well. The veins are 0.1 cm2.5 m in width and 1–60 m in length. They are characterized by a dark gray to gray color and consist of mainly quartz, molybdenite, pyrite and magnetite. Cubanite, pyrrhotite, sphalerite, galena, ilmenite, bornite and bismuthinite are found in minor amounts. Limonite, hematite, marcasite, chalcocite and covellite are secondary products. Potasic alteration zones are common along veins and veinlets. In these zones, disseminated molybdenite and pyrite are also observed. The dissemination type is mainly observed within the biotite- and andalusite–sillimanite granite. Chalcopyrite and pyrite are accompanied by molybdenite. In the Başnayayla, three alteration types have been detected: (a) quartz–sericite–pyrite (phyllic zone), (b) quartz–feldspar–biotite (potasic zone), (c) quartz–feldspar–biotite–sericite/muscovite (potasic–phyllic transition zone). Molybdenum is mainly concentrated in transition and potasic alteration zone. Potasic alteration principally affected biotite granite and two mica granite. This alteration zone contains mainly quartz–K-feldspar–plagioclase–biotite vein/veinlets (0.1 mm–1.5 cm), disseminated magnetite and magnetite–pyrite veins. Pyrite–molybdenite veins and disseminated pyrite are common in the phyllic zone. Quartz–molybdenite veinlets were not detected within the potasic alteration zone. The BY Mo–Cu occurrence is described as a low-grade porphyrytype molybdenum–copper mineralization (Kuşçu and Genç, 1999).

nite, chalcopyrite, pyrite, galena, sphalerite and other sulfide minerals are determined in the vein under the microscope. The Balışeyh molybdenite sample (BLSH-1) was chosen from the E–W oriented quartz vein cropping out on the surface (Fig. 4). The vein is nearly 10 cm in width and contains thin (0.2–0.4 mm thick) molybdenite-rich zones (Fig. 6c). These zones also contain pyrite and chalcopyrite in minor amounts. Molybdenite samples (BM2-11 and BM2-16b) (Fig. 6d) were taken from the BM-2 drill core in Başnayayla. They represent 39.50 and 58.00 m, respectively (Fig. 7). Both samples were chosen from quartz veins crosscutting the biotite granite. Veins are nearly 4 cm in width and mainly contain pyrite with molybdenite. The Re–Os isotope analyses were performed in the Re–Os Laboratory in the Department of Geosciences at the University of Arizona. For each sample, 0.05 g pure molybdenite was loaded into a Carius tube and dissolved with 8 ml of reverse aqua regia. While the reagents, sample, and spikes were frozen, the Carius tube was sealed and left to melt at room temperature. The tube was placed in an oven and heated to 240 °C for 12 h. The solution was processed in a twostage distillation process for osmium separation (Nagler and Frei, 1997). Osmium was further purified using micro-distillation techniques (Birck et al., 1997) and loaded onto platinum filaments with Ba (OH)2 to enhance ionization. After Osmium separation, the remaining acid solution was dried and dissolved in 0.1 HNO3. Rhenium was

4. Sampling and Re–Os analytical techniques For Re–Os age analysis, a total of five molybdenite samples (Fig. 6) were chosen from three different areas [from west to east; two from Karacaali (K2-60, K3-39a), one from Balışeyh (BLSH-1) and two samples from Başnayayla (BM2-11, BM2-16b)]. Karacaali molybdenite specimens were taken from K-2 (sample no: K2-60) and K-3 (sample no: K3-39a) drill cores (Fig. 3). K2-60 represents 141.30 m, whereas K3-39a represents 62.15 m in the drill cores (Fig. 6a, b). Molybdenites in sample K2-60 are taken from quartz–calcite–molybdenite vein (2.5–3 cm-thick) crosscutting porphyritic quartz monzonite and are found together with chalcopyrite, galena and sphalerite. The K3-93a molybdenite sample represents quartz-molybdenite veins (3 cm in width). In addition to molybde-

Fig. 7. Balışeyh Granitoid, simplified geological log of BM-2 drill hole (located on Fig. 5) and sample points for Re–Os chronology (simplified after Kuşçu and Genç, 1999).

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Table 3 Re-Os data for molybdenite from the Karacaali, Balışeyh and Başnayayla occurrences. Sample

Weight (g)

Total Re (ppm)

187

K2-60 K3-39a K3-39a⁎ BLSH-1 BM-2-11 BM-2-16B

0.072 0.076 0.081 0.095 0.013 0.072

16.25 74.78 65.30 4.21 108.86 148.53

12.97 57.88 50.44 3.24 88.01 121.39

Os (ppm)

Age (± 0.4) (Ma) 76.2 73.8 73.7 73.6 77.1 78.0

Decay constant: ʎ (187 Re) = 1.666 × 10− 11 yr− 1 (Smoliar et al., 1996), Uncertainties are calculated using error propagation, considering the error in the decay constant (0.31%), errors in spike calibrations (0.08% for 185Re and 0.15% 190Os), and analytical and weighting errors (Barra et al., 2003; Valencia et al., 2005). ⁎ Replicate analysis.

extracted and purified through a two-stage column using AG1-X8 (100–200 mesh) resin and loaded on platinum filaments with BaSO4. Samples were analyzed by negative thermal ion mass spectrometry (N-TIMS) (Creaser et al., 1991) on a VG 54 mass spectrometer. Molybdenite ages were calculated using an 187Re decay constant of 1.666 × 10 − 11 year − 1 (Smoliar et al., 1996). Uncertainties were calculated using error propagation, which considers the error in the decay constant (0.31%), errors in spike calibrations (0.08% for 185Re and 0.15% 190Os), and analytical and weighting errors (Barra et al., 2003; Valencia et al., 2005). 5. Analytical results The analytical results of five molybdenite samples from Karacaali (2×), Balışeyh (1×) and Başnayayla (2×) are listed in Table 3 and Fig. 8. The analysis of the K3-39a sample from the Karacaali granitoid was performed twice. The concentration of the total Re and 187 Os ranges from 4.21 to 148.53 ppm and 3.24 to 121.39 ppm, respectively. The Re–Os ages of molybdenites (two from Karacaali, one from Balışeyh and two from Başnayayla) are 73.8 ± 0.4 to 76.2 ± 0.4 Ma, 73.6 ± 0.4 Ma and 77.1 ± 0.4 to 78.0 ± 0.4 Ma, respectively. 6. Discussion The Re–Os ages of the Karacaali, Balışeyh and Başnayayla Mo–Cu occurrences, agree well with radiometric ages of the associated granitoids (e.g., Zircon, U–Pb ages 73.1±2.2 Ma for KMC, Delibaş, 2009; Ar–Ar ages 78.1±0.2 Ma and 80.0±0.2 Ma for Yozgat Batholith, Boztuğ et al., 2009) from CACC (Fig. 1). The time interval of Re–Os ages for the different occurrences suggests a coeval event for Mo–Cu mineralizations as compared with the ages of Central Anatolian granitoids (67–110 Ma). Calc-alkaline, I-type Karacaali and I-, S-type Balışeyh and Başnayayla granitic and monzonitic rocks were plotted on the tectonic discrimination diagram of Pearce et al. (1984). In the Rb against Y +

Nb diagram (Fig. 9), Karacaali monzonitic rocks mainly show postCOLG characteristics (Pearce, 1996), whereas Başnayayla and Balışeyh granitic rocks display both post- and syn-COLG granite characteristics, but post-COLG characteristics are more dominant. In this case, ages of the mineralizations (73.6–78.0 ± 0.4 Ma) and also ages and tectonic settings of the host rocks (Karacaali, Balışeyh and Başnayayla) (Table 1) reveal that Mo–Cu mineralizations in the CACC were formed during the post-collisional period. This conclusion is also in accordance with the collision and extension timing of Central Anatolia (Genç and Yürür, 2010). According to Genç and Yürür (2010) crustal thickening and compressional tectonics occurred at Late Cretaceous times and after the Late Cretaceous time the thin-skin extensional tectonics continued to stretch the crust in the region. It is well known that post-collisional granitoids form some of the largest volumes of granite in orogenic belts (Pearce, 1996). Moreover, mantle sourced mafic magma contributions play an important role in their evolution. Recent studies show that I-type and A-type Central Anatolian granitoids are good examples for post-collisional granitoids in the Alpine orogenic belt and show geochemical evidence of mantlederived mafic magma contributions (Delibaş, 2009; Delibaş and Genç, 2004; Delibaş et al., 2011; Kadıoğlu and Güleç, 1996, 1999; Tatar and Boztuğ, 1998;). However, mafic magma contributions in the evolution of post-magmatic ore occurrences/deposits have not been known in Central Anatolia. In recent years, the Re contents of the molybdenites have been used to trace the source of ore materials (Mao et al., 1999, 2003, 2006; Stein et al., 2001). The Rhenium content in molybdenites decreases gradually from the mantle source to a mixture of mantle and crust and then to the crustal source (Mao et al., 1999, 2003, 2006; Stein et al. 2001). In addition, Stein et al. (2001) concluded that deposits with the mantle component (mantle underplating, mantle metasomatism, melting of mafic or ultramafic rocks) have higher Re contents, whereas deposits with a crustal origin have lower Re contents associated with molybdenites. The Re content of molybdenites from the Başnayayla is significantly higher (108.86–148.53 ppm) than the Re contents of molybdenites from the Karacaali (16.25–74.78 ppm) and Balışeyh (4.21 ppm) occurrences. In comparison to cited publications for different locations (e.g., Mao et al., 1999, 2003, 2006, Stein et al., 2001), the Re data of molybdenites from the Karacaali, Başnayayla and Balışeyh may suggest that the Başnayayla occurrence contains more mafic mantle components. It is, therefore, the relatively lower Re contents of molybdenites from the Balışeyh and Karacaali occurrences that may indicate a mixed (crust + mantle) origin, but crustal components are more dominant. Yet, it should also be noted that further Re measurements are needed to constrain definite source of molybdenites from central Anatolia. The new Re–Os ages obtained in this study reflect two mineralization periods: the first, an older event that occurred between 78 and 77 Ma in Başnayala, and the second, a younger mineralization event that occurred between 76 and 73 Ma in Balışeyh and Karacaali (Fig. 8). The data indicate that mineralization developed earlier in the East (Başnayayla)

Fig. 8. Schematic diagram summarizing Re–Os molybdenite ages (bars are ±0.4 of ages).

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of 76.2 Ma, which is very close to Başnayala ages (78 and 77.1 Ma). These two different mineralization periods from the same occurrences and from the same granitic belt cannot be explained by a single magmatic-hydrothermal event. However, the causes of the two different mineralization time intervals could be due to an early molybdenum enrichment related to crystallization processes within the granitic magma and later re-mobilization of the existing molybdenum enrichment within the sub-solidified granitic magma by basic magma injections. Acknowledgments

Fig. 9. The Rb-(Y + Nb) diagram for discriminating the tectonic setting of granites (Pearce, 1996; Pearce et al., 1984). 1: Karacaali; 2: Başnayayla; 3: Balışeyh. Data are from previous studies: 16 samples for Karacaali (Delibaş et al., 2011); 27 samples for Balışeyh (Sözeri, 2003); 12 samples for Başnayayla (Kuşçu and Genç, 1999).

than in the West (Karacaali and Baslışeyh) of central Anatolia. However, one sample taken from Karacaali gives 76.2 Ma, which is very close to the Başnayayla mineralization ages (78 and 77.1 Ma; Fig. 8). The older Re–Os mineralization ages (78.0–77.1 Ma) of the Başnayayla Mo–Cu agree well with the syn-tectonic/collisional characteristics of the Başnayayla granitoids. Close molybdenite and host rock ages (Table 1) obtained from the Karacaali and Başnayayla Mo–Cu indicate a close relationship between mineralization events and granitic magma differentiation and crystallization. Furthermore, the very close zircon and molybdenite ages imply that granitic magma crystallized in a short period of time in shallow crustal levels. The other important conclusion based on the Re–Os age data is the short time period of the mineralization. The time intervals are from 0.9 Ma for Başnayayla in the east and 2.4 Ma for Karacaali occurrence in the west. In comparison with the Başnayayla occurrence, long living mineralization events were active in the Karacaali. The older molybdenite age (76.2 Ma) in Karacaali is close to the age of the molybdenite from Başnayayla (77.1 Ma), and both older ages probably represent the mineralization period related to crystallization–differentiation processes. The younger molybdenite age (73.8 Ma) in the Karacaali may represent prolongation of the life of magmatic-hydrothermal processes/cycles and/ or the remobilization of molybdenum within the solidified granitic system by the intrusion of the basic magma. These findings are also in accordance with the conclusions of Delibaş et al. (2011) in Karacaali Magmatic Complex. 7. Conclusions The Re–Os ages of molybdenite (two from Karacaali, one from Balışeyh and two from Başnayayla) are 73.8 ± 0.4 to 76.2 ± 0.4 Ma, 73.6 ± 0.4 Ma and 77.1 ± 0.4 to 78.0 ± 0.4 Ma, respectively. The Mo– Cu mineralizations age obtained from the Re–Os dating from the molybdenites of Central Anatolia granitoids are consistent with that of the post-collisional granitoid age of the CACC, which indicates the Late Cretaceous (Campanian) period. The Re data of molybdenites from the Karacaali, Balışeyh and Başnayayla may suggest that the Başnayayla contains (108.86– 148.53 ppm) more mafic mantle components. The relatively lower Re contents of the molybdenites from the Balışeyh and Karacaali (16.25–74.78 ppm and 4.21 ppm) indicate a mixed (crust + mantle) origin. Two different time intervals (78–77 Ma in Başnayayla and 76– 73 Ma in Karacaali and Balışeyh) were obtained in this study. These results indicate that the younger mineralization event occurred between 76 and 73 Ma in Karacaali and Balışeyh. However, the older mineralization events developed between 78 and 77 Ma in the Başnayayla area. Moreover, one sample from Karacaali yielded an age

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