Petrology, geochemistry, and evolution of the iron skarns along the northern contact of the Eğrigöz Plutonic Complex, Western Anatolia, Turkey

The Çatak and Küreci skarn districts are located approximately 10 km NW of Emet (Kütahya) in Western Turkey. The skarn and associated ore formations mainly occur at the contact between intrusive rocks of the Eğrigöz Plutonic Complex (EPC) and calcareous pelitic schists with limestone lenses of the Sarıcasu Formation and meta-carbonate rocks of the Arıkaya Formation.

Petrology, geochemistry, and evolution of the iron skarns along the northern contact of

the Eğrigöz Plutonic Complex, Western Anatolia, TurkeyTolga OYMAN*, İsmet ÖZGENÇ, Murat TOKCAER, Mehmet AKBULUT

Department of Geological Engineering, Faculty of Engineering, Dokuz Eylül University, Tınaztepe, Buca, TR−35100 İzmir, Turkey

* Correspondence: tolga.oyman@deu.edu.tr

1 Introduction

In the Cenozoic copious magmatic activity took place in

Western Anatolia and the Aegean region Magmatism was

most widespread and abundant during the oldest phase,

which began in the Late Eocene (about 37 Ma ago) and

ended in the Middle Miocene (about 14–15 Ma ago) It

is represented by volcanic and plutonic rocks of orogenic

affinity The Eybek, Kozak, Alaçam, and Eğrigöz

volcano-plutonic centres, predominantly consisting of intrusive

rocks, are the main examples of this early phase (e.g., Yılmaz

1990) The Eğrigöz Plutonic Complex (EPC) is situated

inland in Western Anatolia within the core and cover

sequences in the northeastern part of the Menderes Massif (Figure 1) The EPC, with an outcrop area of approximately

550 km2, is one of the largest plutons in western Turkey, and is associated with a number of mineral occurences including iron skarns, Au-Ag-bearing mesothermal Pb-

Zn-Cu veins, skarns and gossans (Özgenç et al 2006) The

district has been of economic interest since the second half

of the 20th century, and the magnetite resources around the EPC are becoming increasingly important Recent geochronological studies focused on the crystallizing and cooling ages of the Eğrigöz granite and yield ages around

20 Ma (Işık et al 2004; Ring & Collins 2005; Hasözbek et

Abstract: The Çatak and Küreci skarn districts are located approximately 10 km NW of Emet (Kütahya) in Western Turkey The

skarn and associated ore formations mainly occur at the contact between intrusive rocks of the Eğrigöz Plutonic Complex (EPC) and calcareous pelitic schists with limestone lenses of the Sarıcasu Formation and meta-carbonate rocks of the Arıkaya Formation The major, trace, and rare earth element analysis of the igneous rocks indicate that they are high level, subalkaline, calc-alkaline, peraluminous to metaluminous I-type intrusions, generated in a continental arc setting Three distinct skarn-type mineralization, differing in their host rocks and distance from the intrusive body, were chosen to establish the ore-forming conditions in different episodes of skarn formation The Küreci iron mineralization is hosted in a skarn zone with well-developed zoning from unaltered granodiorite and endoskarn, andradite-diopside exoskarn, to diopside-wollastonite exoskarn towards a marble reaction front In Sakari, the iron mineralization and associated skarn have formed due to successive fracturing and infiltration processes From early contact metamorphic rocks to

characteristic, with its high sulphide content due to the presence of pyrrhotite, pyrite, and arsenopyrite, and low proportion of garnet

interpret the bulk of the sulphur in the system as of igneous derivation and there has not been any significant sulphur contribution from

a crustal source Fluid inclusion measurements conducted on skarn minerals of the proximal zone and distal zone+vein skarn revealed high homogenization temperatures (371 to >600°C) and varying salinity values (10.5 to >70 wt% NaCl) The fluid inclusion data indicate that there are at least three fluids associated with the genesis of the proximal skarn where the high garnet/pyroxene ratios are found Fluid inclusions that represent the early stages both in garnet and pyroxene plot in ‘Primary Magmatic Fluid’ and ‘Metamorphic Fluids’ fields A magmatic fluid, presumably located at deeper parts of the system, mixed with a metamorphic fluid during its ascent Over all the Eğrigöz skarn a weak or moderate retrograde skarn alteration envelope formed, dominated by the incursion of meteoric waters

in the system, indicating limited fluid-rock interaction Hydrofracturing resulted in pressure decrease and inclusions with Type III (L+V+S) inclusions that plot in the ‘Secondary Magmatic Liquid’ and ‘Magmatic Meteoric Mixing’ fields.

Key Words: geochemistry, iron skarn, calc-silicate, Eğrigöz, Turkey

Received: 01.06.2010 Accepted: 30.06.2011 Published Online: 04.01.2013 Printed: 25.01.2013

Research Article

CRETACEOUS TRIASSIC JURASSIC MESOZOIC PALEOZOIC

QUA TERNAR Y

aspects of the economic potential of the district, studies

of ore and calc-silicate paragenesis and stable isotope

studies are lacking (Gümüş 1967; Özocak 1972; Taşan

& Cihnioğlu 1984) The aim of this study is to examine

the characteristics of this important, but otherwise little

known iron district and develop a model for its genesis

For this purpose we focus on several iron deposits (Sakari,

Çatak, and Küreci) along the northern contact of the EPC,

which have representative ore and gangue paragenesis

for the mineralization of the northern contact In these

deposits we describe the presence of changing redox

conditions in ore-forming magmatic-hydrothermal

systems based on the mineral chemistry of calc-silicates

(e.g., garnet, pyroxene, amphibole) and associated

sulphides of Cu, Fe, and As (e.g., chalcopyrite, pyrrhotite,

arsenopyrite) Compositional variations in calc-silicate

mineralogy reflect differences in magma chemistry, wall

rock composition, depth of formation, and oxidation

state (Burton et al 1982; Gamble 1982; Meinert 1992,

1997) Fluid inclusion data, together with petrological and

isotopic information, may provide complete information

for knowing the P and T evolution of the skarn system

Although the Sakari, Çatak, and Küreci iron skarns

are all spatially and genetically related to the EPC, the

differences in skarn texture, paragenesis, and geochemistry

are significant Geochemical studies on ore and coexisting

calc-silicates in prograde stage or hydrous calc-silicate

overprint related to hydrothermal fluids give important

clues on the heat and fluid transfer from a cooling magma

Rare earth element (REE) mobility is favoured by low

pH, high water/rock ratios, and abundant complex ions

(CO3–2, F–, Cl–, PO43–, SO42–) in the hydrothermal solutions

(Michard 1989; Lottermoser 1990, 1992) REE contents of

hydrothermally altered rocks in epithermal and porphyry

copper ore deposits indicate that fluid alteration is an

important agent in the mobilization of REE (Lottermoser

1990; Hopf 1993; Arribas et al 1995; Bierlein et al 1999;

Fulignati et al 1999) Skarn systems adjacent to granite are

the most likely sources of the REE and speciation control on

the uptake and deposition of the REE from hydrothermal

fluids of different temperatures and composition (Smith et

al 2000) Wang & Williams (2001) noted that REE were

transported in skarn-forming fluids and that their current

distribution is influenced by the occurrence of phases,

such as allanite and apatite in Cu-Au (Co-Ni) skarns in

the Cloncurry district in Queensland, Australia REE

contents of ore samples from Pena Colorado iron skarns

in Colima, Mexico represent those of the andesitic tuffs

of the volcano-sedimentary rocks (Zürcher et al 2001)

Trace, and rare earth element (REE) abundances provide

an opportunity to investigate the interaction between the

mineralizing fluids and the host rocks, with the chemistry

the type of the deposit

In this paper, we present new geochemical data from the host granite and ore, including compositions of skarn minerals, microthermometric studies on skarn minerals and isotope determinations (S isotopes from pyrite and pyrrhotite and O isotopes from magnetite, pyroxene, and garnet) Based upon this data, we interpret the formation conditions of the various iron skarns with different paragenetic, spatial and temporal characteristics related to the emplacement of the EPC

2 Geologic and tectonic setting of Western Anatolia

The geological evolution of Western Anatolia was mainly governed by Palaeo- and Neo-Tethyan events, which preserve remnants of the Tethyan ocean The Neotethys Ocean was obliterated by the collision of the Eurasian and African plates mainly during the Late Cretaceous–Tertiary (Şengör & Yılmaz 1981; Şengör 1987) As a remnant of Neotethys, the İzmir-Ankara Melange zone separates the Sakarya Zone and the Anatolide-Tauride Block now exposed in the metamorphic core complex of the Menderes Massif Intrusion of Palaeogene granitoids in the Sakarya Zone, the İzmir-Ankara mélange zone, and the Menderes Metamorphic core complex are linked by the subduction

of the East Mediterranean ocean floor, along the Hellenic

trench (Fytikas et al 1984; Pe-Piper & Piper 1989; Gülen

1990; Delaloye & Bingöl 2000) The convergence has been generated in a N–NE direction by subduction along the Aegean and Cyprean arcs in the western and eastern Mediterranean, respectively The Menderes metamorphic core complex has undergone five phases of metamorphism (Bozkurt & Oberhänsli 2001) The age of the main metamorphism affecting the whole massif is Palaeocene–Eocene (Satır & Friedrichsen 1986; Hetzel & Reischmann

1996; Bozkurt & Satır 2000; Lips et al 2001; Rimmele et al

2003; Bozkurt 2004) Intracontinental N–S convergence associated with the Palaeocene–Eocene collision along the İzmir-Ankara suture zone continued until the Oligocene During the early Miocene, crustal thinning in the central Menderes Massif was associated with the denudation

of the core complex in the footwalls of the Gediz and Büyük Menderes detachment faults (Emre & Sözbilir

1997, 2007; Lips et al 2001) These comprise mylonitised,

metamorphic, and granitic rocks lying below a low-angle detachment fault, with associated chlorite brecciation and two supradetachment basins containing a thick succession

of nonmarine strata (Hetzel et al 1995; Emre & Sözbilir 1997; Koçyiğit et al 1999; Sözbilir 2001, 2002; Seyitoğlu et

al 2002; Işık et al 2003, 2004; Bozkurt & Sözbilir 2004)

The footwall metamorphic rocks were progressively mylonitised, exhumed, and intruded by syndeformational granitoids (Turgutlu and Salihli granodiorites: the Salihli

biotite plateau cooling ages of 19.5±1.4 and 12.2±0.4 Ma,

respectively) (e.g., Hetzel et al 1995; Koçyigit et al 1999;

Lips et al 2001; Sözbilir 2001, 2002; Seyitoğlu et al 2002;

Işık et al 2003, 2004; Bozkurt & Sözbilir 2004) Different

models were proposed to explain the origin and timing of

the extension and granitoid intrusions in western Turkey

The back-arc spreading (Le Pichon & Angelier 1979, 1981),

the tectonic escape (Şengör 1979; Şengör et al 1985) and

the orogenic or gravitational collapse model (Dewey 1988;

Seyitoğlu & Scott 1996) are the proposed models The

Tertiary magmatism in Western Anatolia consisted of

three geochemically distinct phases of magmatic activities

due to S–SW retreat of the active subduction zone

(Doglioni et al 2002; Innocenti et al 2005) The oldest

phase of the magmatic activity in western Anatolia, which

began in the Late Eocene (at about 37 Ma) and ended in

the Middle Miocene (at about 14–15 Ma), is represented

by volcanic and plutonic rocks of orogenic affinity The

Eybek, Kozak, Alaçam, and Eğrigöz volcano-plutonic

centres, predominantly consisting of intrusive rocks, are

the main examples of this early phase (e.g., Yılmaz 1990)

Radiometric dating of the synextensional granites, which

intrude the Menderes Massif and Afyon Zone, are Early

Miocene in age K-Ar age determination by Delaloye &

Bingöl (2000) shows that the subduction event must have

commenced before the Oligocene Based on their K-Ar

age determinations on biotite and orthoclase from the

Eğrigöz granitoid, cooling ages were obtained of 20.0±0.7

to 20.4±0.6 Ma and 21.2±1.8 to 24.6±1.4 Ma, respectively

The EPC was emplaced during the late stage of mylonitic

deformation of the extensional tectonic regime and was

deformed along the boundary of core rocks of the MCC

(Işık et al 2004) On its northern and western boundary,

the Eğrigöz granitoid is separated from the cover series by

the Simav detachment fault (Işık et al 1997; Işık & Tekeli

2001; Erkül 2010) (Figure 1) The cover sequences of the

MCC consist mainly of schist, recrystallized carbonates,

and ophiolitic mélange which experienced varying grades

of metamorphism Intrusion and cooling of the Eğrigöz

granitoid occurred at 22.86±0.47 Ma (40Ar/39Ar ages, Işık

et al 2004) More recently, U-Pb zircon analyses have

yielded crystallization ages of 19.4±4.4 Ma for the Eğrigöz

granite (Hasözbek et al 2010) A cooling age of 18.77±0.19

Ma for the Eğrigöz granite was obtained by Rb–Sr (whole

rock, biotite) analyses

3 Local geology

The oldest country rocks surrounding the Eğrigöz granitoid

are the Simav metamorphic sequence, which is exposed

southeast and west of the Eğrigöz Pluton (Figure 1) This

unit is comprised of biotite-muscovite schists,

muscovite-quartz schists, garnet schists, muscovite-muscovite-quartz-biotite

schists (Akdeniz & Konak 1979) The Balıkbaşı Formation conformably overlies the Simav metamorphics in the south

of the EPC, and is comprised of laminated, bituminous recrystallized limestone reflecting neritic facies conditions The Balıkbaşı Formation is uncomformably overlain by Upper Palaeozoic–Lower Triassic Sarıcasu Formation, mainly comprising schists that are metamorphosed greenschist grade equivalents of detrital sediments with basic tuffs and lavas These schists were first identified

by Kaya (1972) as part of the İkibaşlı Formation and are equivalent to the Sarıcasu Formation of Akdeniz & Konak (1979) The Sarıcasu Formation is gradationally overlain

by the Arıkaya Formation that outcrops widely around the village of Küreci Based on lithological correlation between the Arıkaya Formation and fossiliferous Permian limestone and its boundary with overlying fossiliferous Middle–Upper Triassic rocks, the age of the formation has been thought to be Permian (Akdeniz & Konak 1979) The limestone lenses in pelitic schists and the meta-carbonate rocks of the Arıkaya Formation are important host rocks for magnetite and pyrrhotite skarns

3.1 Host rocks

Aureoles associated with EPC commonly show conspicuous evidence of metasomatic processes related to local injection of magma or hydrothermal fluids into country rocks The skarn zone between the Eğrigöz pluton and the surrounding Palaeozoic Sarıcasu and Arıkaya formations extends ~3.5 km along the contact and is ~10 to ~100 m

wide The skarn bodies in Çatak are hosted by both the

Palaeozoic Sarıcasu and Arıkaya formations, but the bulk

of the ore bodies lie within the Sarıcasu Formation (Figure 1) This unit consists of muscovite-quartz-albite schist, and muscovite-chlorite-calcite-quartz schist intercalated with phyllite and crystalline limestone Phyllite intercalated with schists crops out near the village of Gürepınar The phyllite has well-developed cleavage, and is composed of quartz, plagioclase, sericite, chlorite, titanite, and opaque minerals Recrystallized limestone lenses appear within the schist sequence One of the the largest outcrops of these lenses is observed around the Elçekkaşı ridge The limestone is fine grained and grey We speculate that hydrothermal fluids migrated along pre-skarn fractures, sedimentary contacts, and other permeable zones until they reacted with the schist intercalated with carbonate-rich intervals in the Sarıcasu Formation Successive fracturing and infiltration of more evolved mineralizing fluids may have destroyed the original spatial zonation.Along the northern border of the Eğrigöz Pluton close to the contact, the rock is hornfelsed in a 10- to- 120-m-thick zone identified by its fine schistosity and dark green to olive green colouration Besides the more

common porphyroblastic schists, minor mica-rich

varieties with lepidoblastic fabric and quartzo-feldspathic

varieties were observed Albite porphyroblasts, quartz with

undulatory extinction, calcite, muscovite, chlorite, pyrite,

and magnetite are the main constituents of the schist The

schistosity strikes mainly NE with variable dips of 30–60°

NW Muscovite-quartz-albite schist was typically observed

along the eastern contact of the Eğrigöz pluton The schist

generally possesses medium-high strength with medium

to coarse schistosity The rock has a porphyroblastic texture

with quartz and albite porphyroblast lengths exceeding 3

cm The porphyroblast-hosted matrix consists mainly of

muscovite and minor amounts of epidote, calcite, and

chlorite

The Arıkaya Formation is a bedded package of

recrystallized limestone with a dense joint system,

intensely developed fold structures, and local brecciation

Recrystallized limestones with grain sizes up to 2 mm

are common, and the limestone is locally dolomitic The

ore-bearing calcic skarn is located at the northern contact

zones with granodiorite

3.2 Plutonic rocks

The plutonic rocks in the region have a holocrystalline,

hypidiomorphic texture with quartz, plagioclase,

orthoclase, biotite, and hornblende as major

rock-forming minerals Apatite, zircon, titanite, and muscovite

are common accessory phases The opaque minerals

(e.g., magnetite, pyrite), chlorite, sericite, epidote, and

tourmaline are present, but less common Fine-grained

plutonic varieties were observed close to the contact with

the skarn Aplitic dykes of the EPC cross-cut plutonic

rocks associated with magnetite deposits at the eastern

and southern contacts, whereas in the centre and northern

part of the pluton, dykes are associated with polymetallic

veins

Selected whole-rock analyses of 10 samples from

the EPC are listed in Table 2 In total 68 fresh, coarse-

to medium-grained phaneritic granitoid samples were

collected from the northern part of the EPC and 10 of

them were selected, based on their location near the

mineralization sites In the QAP molecular normative

diagram (Streckeisen 1976), the rocks plot in the

monzogranite and granodiorite fields with a transitional

trend (Figure 2a) and in the Q-P diagram (Debon & Le Fort

1983), plot in the granodiorite and adamellite field (Figure

2b) The granitoids are plotted on the boundary between

the metaluminous and peraluminous granitoid fields in

an aluminum saturation diagram (Maniar & Piccoli 1989)

(Figure 2c) The granitoid rocks are calc-alkaline on the

Na2O+K2O–CaO versus SiO2 diagram (Frost et al 2001)

(Figure 2d) The chondrite-normalized REE patterns

for EPC granitoids related to iron skarns are shown in

Figure 2e (normalizing values after Sun & McDonough

1989) The granitoids exhibit moderate LREE fractionated patterns with a negative Eu anomaly (Eu/Eu*= 0.44–0.61) They show nearly flat HREE patterns with Tb/Ybn

~1.2 Transitional trends from pre-plate collision to collision settings of granitoids are distinctive in Figure 2f

syn-The Rb vs Nb+Y diagram (Pearce et al 1984) emphasizes

that the granitoids are volcanic arc granites (Figure 2h) and plot in the volcanic arc + syn-collision field in the Nb-Y diagram (Figure 2h)

4 Contact metamorphic assemblages

The limestone lenses in pelitic schists of the Sarıcasu Formation and the meta-carbonate rocks of the Arıkaya Formation are important host rocks for magnetite and pyrrhotite skarns in the Çatak region Early distal isochemical metamorphism caused the formation of calc-silicate hornfels and marble Hornblende-biotite hornfels contains quartz, hornblende, biotite, plagioclase, muscovite, and andalusite Pyroxene hornfels contains diopside, garnet, plagioclase, K-feldspar, biotite, cordierite, and sillimanite Metamorphosed carbonate rocks include marble Metamorphism of pelitic schists and calcareous rocks has produced an assemblage of andalusite, cordierite, sillimanite, feldspar, biotite, tourmaline, and quartz The presence of cordierite, andalusite, and sillimanite imply metamorphic temperatures of 500°C and a maximum pressure of 2kb (Winkler 1967; Mason 1990) Stabilities of calc-silicate assemblages depend on mole fractions of CO2 in the aqueous phase, as well as

on pressure, temperature, and the composition of solid solution minerals (Sato 1980; Newberry 1982; Meinert 1982) If CO2 was near 0.1 kb during the metamorphism and early skarn formation, a minimum temperature of 550°C is required for grossularite and wollastonite stability

at 2 kb (Greenwood 1967; Gordon & Greenwood 1971; Meinert 1982) A minimum temperature of 550°C is also required for the presence of diopside in pyroxene hornfels

As prograde alteration reflects the protoliths, pelitic schists are represented by hornblende hornfels, calcareous rocks by pyroxene hornfels and meta-carbonate rocks by pyroxene-garnet skarns

The pyroxene hornfels facies is developed within a restricted zone close to the contact with the pluton The presence of sillimanite indicates pyroxene-hornfels facies conditions and aluminum rich protoliths (Winkler 1967) The paragenesis in the pyroxene-hornfels facies comprises cordierite, pyroxene, garnet, plagioclase, sillimanite, orthoclase, biotite, titanite, apatite, chlorite, and quartz The hornblende hornfels facies is characterized by the occurrence of andalusite, amphibole, biotite, muscovite, quartz, and subordinate plagioclase, calcite, chlorite, apatite, tourmaline, axinite, titanite, and zircon Typical pressures for the hornblende hornfels are less than 4

Weight % CT-1 CT1-8 CT1-13 CT1-14 CT2-22 CT2-23 CT3-7 OC1-26 KUR1-7 KUR-14 KB-1

kilobars, and temperatures range between 400 and 650°C

The existence of andalusite indicates low- to

intermediate-grade metamorphism in the surrounding aureole With

increasing distance from the contact aureole, greenschist

facies regionally metamorphosed rocks represent the

cover series

5 Skarn mineralogy and paragenesis

More than 30 iron skarn occurences are known in the

Sarıcasu and Arıkaya formations, of which 12 had been

mined between 1950 and 1970 In Çatak district, the

area along the northern contact of the EPC contains

more than 15 iron deposits The Çatak iron skarn district

consists of several bodies that include: Sakari, Çavdarlık,

Göğez, and Katranlı (Figure 3) Among these zones of

mineralization, the Sakari prospect differs because it

is a magnetite-dominated ore, compared to the other

prospects in the Çatak district In the Katranlı, Göğez,

and Çavdarlık prospects, iron mineralization occurs

commonly as tabular bodies and lenses associated with

disseminated and stockwork-type deposition Subordinate

small crosscutting veins and veinlets are also present The

mineralization is closely associated with metasomatic

skarn consisting mainly of pyroxene, garnet, plagioclase,

amphibole, epidote, calcite, and quartz, preferentially

replacing pyroxene hornfels facies rocks between 10 to 100

m from the Eğrigöz granodiorite

5.1 Mineralogy of skarn in the Katranlı, Göğez and

Çavdarlık districts

A narrow reaction zone (20 cm to 1.5 m thick) is developed

in the Göğez and Çavdarlık endoskarn toward the proximal

zone of the pluton (Figure 4) At the contact, the granite is

a darker greenish colour due to the metasomatic reaction

with the wall rock pyroxene hornfels Chlorite, amphibole,

and epidote are the characteristic metasomatic minerals

in the endoskarn Fracture-controlled metasomatism is

the most common replacement mechanism Chlorite and

amphibole, as pseudomorphs of pyroxene, are the main

calc-silicate minerals associated with opaque minerals in

these fracture fillings Disseminated anhedral to subhedral

opaque crystals are mantled by chlorite crystals in the

endoskarn Epidote and plagioclase are associated with

chlorite and amphibole to a lesser extent The plagioclase

is replaced by epidote and calcite Biotite is also replaced

by chlorite and amphibole pseudomorphs Some

disseminated anhedral ore minerals occur, which are

hematitized and limonitized

The calcic exoskarn is composed chiefly of pyroxene

with subordinate garnet and amphibole Microprobe

analyses were performed mainly on pyroxene, garnet,

amphibole, pyrrhotite, chalcopyrite, and arsenopyrite

Details of the analytical methods of microprobe analysis

are given in the Appendix

Garnet and pyroxene crystals are fractured and crosscut

by veinlets of late stage ore and retrograde minerals Euhedral to subhedral pyroxene is the earliest calc-silicate mineral of the prograde stage with the grain size ranging between 20 µm and 1 mm Pyroxene grains within the exoskarn range between hedenbergitic and diopsidic end members with an average composition of Di43–53 Hd46–56

Jo1–2 (Figure 5a; Table 3) Optically and compositionally zoned individual garnet grains typically are 10 µm – 3

mm in diameter In the exoskarn zone, garnet is andradite (Ad97–99) within a narrow compositional range (Figure 5b; Table 4) Pyroxene grains are extensively included

in garnet, magnetite, and pyrrhotite as relict crystals Pseudomorphic amphibole replacement after pyroxene

is the most common retrograde alteration, followed by the replacement of the epidote, chlorite, and prehnite as vein-fillings The composition of amphiboles varies within the calcic amphibole types (Na+K<0.5) Based on Leake

et al (1997), amphibole compositions from Çatak plot as

actinolite-ferroactinolite and Mg hornblende Amphiboles

of the Çatak pyrrhotite skarns have higher Mg, Si, and lower Al values than those of the Sakari magnetite skarns.Tourmaline with high magnesium and aluminum contents (dravite) is common in the surrounding schist and hornfels, suggesting a metasomatic origin related

to early contact metamorphism Pyrrhotite, magnetite, pyrite, and chalcopyrite in descending order are abundant ore minerals Accessory minerals include arsenopyrite, gersdorffite, melnicovite pyrite, linnaeite, ilmenite, and rutile Magnetite follows coarse crystalline pyroxene-garnet skarn as an early ore phase Exsolution lamellae

of ilmenite in magnetite appear as a function of oxygen fugacity and temperature and are probably related to the cooling stage of igneous activity

Sulphides always post-date magnetite precipitation (Figure 6a) Pyrrhotite developed between the euhedral granular magnetite crystals and replaced magnetite along their crystal edges Lamellar intergrowth of pyrrhotite with linnaeite is a common ore texture in the ore zone (Figure 6b) Pyrrhotite and/or pyrite-pyrrhotite veinlets crosscut the early magnetite In some samples, pyrrhotite forms as

a prograde texture as rhythmically banded features with retrograde amphibole, which replaced prograde pyroxenes Chalcopyrite commonly replaces pyrrhotite and also fills pyrrhotite-pyrite interstices (Figure 6c) As a late stage event, melnikovite pyrite replaces both pyrrhotite and chalcopyrite Replacement of pyrrhotite by melnikovite pyrite resulted in the development of well-developed ‘bird’s eye’ texture (Figure 6d) Alteration of pyrrhotite along its grain boundaries is a common hydrothermal process The porous texture of this secondary pyrite (melnikovite pyrite) indicates appreciable volume decrease during replacement (Figure 6c, d) Melnikovite pyrite also formed

Figure 2 Plots comparing the major and minor element contents of plutonic rocks of the EPC (see Table 1 for data) (a) Normative

compositions of granitoids plotted on the classification diagram of Streckeisen (1976) Q= quartz; A= (Or); P= (Ab + An); (b) Plot (after Debon & Le Fort 1983) displaying the mean composition of of the plutonic rocks; (c) A/NK vs A/CNK diagram, after Maniar &

Piccoli (1989); (d) Modified alkali versus silica plot showing the calc-alkaline affinity of the plutonic rocks, after Frost et al (2001); (e)

Chondrite-normalized rare earth element patterns of plutonic rocks Normalization values from Sun & McDonough (1989); (f) element geotectonic discrimination diagrams of the plutonic rocks; (g, h) Trace element geotectonic discrimination diagrams (Pearce

a a-c c-a c diorite quartz diorite tonalite trondjhemite granodiorite

alkali feldspar granite granite

42 40

as a replacement of iron-rich calc-silicates (Figure 6e) Due

to the intense deformation euhedral to subhedral pyrites

and arsenopyrites are both fractured Pyrite crystals are

rimmed with arsenopyrite which is also precipitated in

fractures of pyrite (Figure 6f)

Late stage hydrothermal events represented by

fissure-controlled veins clearly cut the sulphide precipitation and

surrounding skarn zone Quartz veins with chalcopyrite

blebs have mantled the clasts of pre-existing ore minerals

Native gold is associated with quartz in some samples

Supergene effects include martitization of magnetite,

replacement of chalcopyrite and pyrrhotite by goethite

(Figure 7)

5.2 Sakari prospect

The geometry and the zonation of the skarn in Sakari

Tepe (Çatak District) is shown in Figure 8 At Sakari,

the mineralization and associated skarn were formed by

successive fracturing and infiltration processes, although

the contact with the intrusive rock is not exposed The

skarn forms lenticular bodies and exhibits a gradual

contact with hornfelsic wall rocks The deposit consists

of a zoned body, in which the central core is a

pyroxene-garnet dominated, coarse-grained skarn associated with

massive ore Pyroxene is the earliest calc-silicate mineral

that precipitated, due to interaction of a calcareous host

rock with ore-bearing metasomatic fluids (Figure 9a)

In the central core early pyroxene in magnetite-bearing

skarn is diopside (Di50–70 Hd28–53 Jo1–2) (Table 3, Figure

5a) In the central core early pyroxene is replaced by

magnetite and subordinate amounts of garnet (Ad95–99

Gr1–5) (Table 4) Pyrrhotite is the early sulphide mineral

that replaces prograde stage iron-bearing calc-silicates, chiefly andradite (Figure 9b) The early stage pyroxene-magnetite-garnet association is both replaced and crosscut

by late stage, anisotropic garnet (Ad36–58 Gr40–61) (Figure 5b) and hedenbergitic pyroxene (Di19–73 Hd26–77 Jo2–6)

In the garnet-dominated coarse-grained magnetite skarn, crosscutting pyroxene has a hedenbergite-rich composition (Di19–73 Hd26–77 Jo2–6) In some places pyroxene grains are replaced by amphibole, and both are replaced by scapolite Scapolite is also found as fracture and vug filling fine-to coarse-grained crystals (>0.5 mm) Quartz, epidote, chlorite, and rarely amphibole are the main retrograde phases and they occur either in a fracture network, which crosscuts or replaces the prograde skarn mineral assemblage Epidote is the most common retrograde calc-silicate, and grossular is the dominant prograde calc-silicate (Figure 9c)

The main ore-bearing skarn zone grades into distal banded hornfels, composed of pyroxene, amphibole-bearing mafic layers and plagioclase, quartz, K-feldspar, and cordierite-bearing felsic horizons The mineralogy probably reflects the lithological control of its protolith during metasomatism Pyroxene from the contact metamorphic zone close to granodiorite is diopside (Di49–76 Hd24–53), associated with epidote, albite, and amphibole Monomineralic diopside horizons probably replace former thin carbonate intercalations, whereas the polymineralic layers are developed over pre-existing impure greywackes Diopsidic hornfels is the early calc-silicate, which is replaced mainly by amphibole in bands The metasomatic fluids crystallizing pyroxene were not as

CT-1 CT1-5

SK-4

Figure 4 Cross section displaying contact between plutonic rocks and the pyrrhotite-dominated Göğez iron skarn in the Çatak district.

enriched in Fe2+ and Mn as those of coarse-grained skarn

with massive ore Fine-grained granoblastic plagioclase is

replaced by pseudomorphs of epidote in the plagioclase,

quartz, cordierite, sillimanite, and K-feldspar-bearing

bands of the hornfels

The massive ore is dominated by euhedral magnetite

with crystal sizes ranging from 0.5 mm up to 2 mm

Pyrrhotite, chalcopyrite, pyrite, and ilmenite are accessory

ore minerals Sulphides constitute more than 10 percent of

the massive ore and post-date magnetite precipitation We

speculate that the magnetite was deposited in at least two

stages First, replacement of calc-silicates by magnetite is

the earliest and commonest event in the ore precipitation

stage Following the deposition of prograde magnetite,

pyrrhotite appears, due to replacement of either magnetite

or iron-rich calc-silicates preferentially (Figure 9d) The

replacement textures in magnetite and/or pyrrhotite in

calc-silicates and pyrrhotite in magnetite are characteristic

features of deposition stages The fractures resulting

from the intense deformation of magnetite and the

wall rock are filled by later sulphides, mainly hexagonal

pyrrhotite, chalcopyrite, and subordinate pyrite (Figure

9e, f) In this second stage, pyrrhotite was intergrown

with chalcopyrite and was subsequently replaced by

chalcopyrite Where chalcopyrite is the only sulphide

phase, it appears to fill cavities, fractures and crystal

boundaries of granular magnetite Exsolution lamellae

of ilmenite in metasomatic magnetite are a function of

oxygen fugacity and temperature related to the cooling

stage of igneous hornfels activity (Gasparrini & Naldrett

1972) Buddington & Lindsley (1964) first pointed out that

coexisting equilibrated pairs of titaniferous magnetite and ilmenite may permit simultaneous determination of the temperature and oxygen fugacity at the time of formation

In Sakari rarely-observed fine-grained ilmenite crystals were found as inclusions in magnetite and pyrrhotite Alteration of ilmenite to rutile is a common process Hematite and goethite after magnetite and goethite after hematite and siderite are the main products of supergene alteration (Figure 10) Hematite is relatively more abundant and may form massive bodies as a replacement phase

6 Skarns in the Küreci district

The geological map of the Küreci mineralization is shown in Figure 11 The Küreci magnetite-specularite mineralization consists of two main skarn bodies including Maden Tepe and Karataş Tepe In Maden Tepe, the extent

of the exoskarn zone may reach ~10 to ~50 m, whereas the endoskarn zone is quite narrow up to a few metres The skarn zonation is: unaltered granodiorite, endoskarn, andradite-diopside-magnetite skarn, magnetite, diopside-wollastonite skarn, and recrystallized limestone (Figure 12) The presence of wollastonite at the limestone front suggests that the bulk of prograde skarn formation occurred at temperatures between 550 and 600°C; within the wollastonite stability field (Meinert 1982)

Granodiorite in the area can be affected by widespread alteration due to the intense fracturing along the contact with the Arıkaya Formation The endoskarn is dominated

by plagioclase replacement after K-feldspar, chlorite after amphibole, biotite, and plagioclase in the early skarn Fine-grained myrmekitic intergrowths occur in endoskarn zones near contacts Primary biotite and amphiboles in the granodiorite are totally obliterated, whereas chlorite and Fe-oxides were also precipitated along fractures and/

or crystal boundaries of plagioclase The outer shell of the granodiorite gains a darker greenish colour due to gradual increase of chlorite towards the exoskarn Magnetite and pyrite appear as euhedral small grains disseminated throughout the endoskarn (Figure 13a)

The host rock of the calcic skarn is mainly limestone

of the Permian Arıkaya Formation The calcic skarn assemblage is characterized by coarse, crystalline, prograde garnet and pyroxene The early stage of skarn development is characterized by a well-developed garnet skarn zone that extends ~25 m further out from the contact of the intrusion Garnets are andraditic (Ad95–99) (Table 4) The massive garnet skarn locally contains patches of magnetite and pyrite associated with retrograde minerals (e.g., quartz, calcite, and chlorite) within cavities and fractures (Figure 13b) The proportion of pyroxene increases gradually towards the limestone (Figure 13c, d) At the limestone contact, the skarn is represented by

a wollastonite-bearing zone, which can be several metres

Çatak skarn Sakari hornfels Küreci skarn

Sakari prograde skarn Stage II Sakari prograde skarn Stage I

b

a

Figure 5 Ternary diagrams showing compositional variations of

clinopyroxene (a) and garnets (b) from the iron skarns

associated with the EPC.

thick Massive magnetite ore and associated magnetite

veinlets are more common in pyroxene and

wollastonite-dominated skarns

The Karataş Tepe mineralization differs from the Maden

Tepe district in its distinct emplacement, paragenesis, and

evolution Specularite-quartz veins that cut the hornfels

have a N25°E strike with an average dip of 40°W The

paragenesis of the vein is quite simple Specularite is the

main ore mineral with subordinate amounts of pyrrhotite,

ilmenite, rutile, chalcopyrite, pyrite, goethite, and siderite

The surrounding rock was intensively silicified along

its contact with the vein Specularite occurs as elongate

euhedral crystals 0.5 to 0.9 mm long with lamellar

twinning Fine needles of specularite interstitial with

quartz are widespread Rutile is a common ore mineral and pseudomorphous anatase after rutile is common Pyrrhotite is rare, with individual crystals situated between elongate specularite Their grain sizes typically range between 5–100 µm Textural relationships indicate that specularite precipitation is sequentially overprinted

by fine-grained polygonal quartz crystals (Figure 13e) Sericitization is superimposed and localized in the vein and neighbouring fracture zones Specularite is replaced

by goethite along its margin throughout the vein (Figure 13f) Rarely observed anhedral chalcopyrite and euhedral pyrite is also replaced by goethite The whole process was terminated by the pseudomorphous replacement of goethite by siderite

Table 4 Selected results of electron microprobe analyses of garnets of the Çatak, Sakari and Küreci districts.

7 Fluid inclusion studies

Fluid inclusion measurements were conducted on primary

inclusion assemblages of clinopyroxene and garnet mainly

in proximal zones of the exoskarn In the 10 samples from

the Çatak and Kureci areas, only primary fluid inclusions

yielded what we consider to be reliable homogenization

temperatures (Th) and final ice melting temperature

(Tm-ice) measurements The results are summarized in Table

5 and Figure 14 Three different types of inclusions were identified in garnets, based on room temperature phase properties: (1) Type I inclusions are two phases (liquid + vapor) and liquid-rich at room temperature; (2) Type II inclusions contain two phases (liquid + vapor) and are vapor-rich at room temperature and (3) Type III inclusions

cpy

silicate

calc-asp py

mt

Figure 6 Photomicrographs of skarn assemblages from the Çatak district (a) Pyrrhotite (po) dominated

sulphide-filled fractures cutting the pre-existing magnetite (mt); (b) Lamellar intergrowth of pyrrhotite (po) with linnaeite

(ln) and replacement of pyrrhotite by chalcopyrite (cpy) are common ore textures; (c) Infilling of interstices between

pyrrhotite (po) and pyrite (py) with bird eye texture by chalcopyrite (cpy); (d) The porous texture in melnikovite

pyrite (py) after pyrrhotite (po); (e) Melnikovite pyrite (py) formation as a replacement of iron-rich calc-silicates; (f)

Euhedral to subhedral pyrite (py) crystals are coated with later arsenopyrite (asp).

are multiphase (liquid + vapor + solid) inclusions They

contain solid crystalline phases known as daughter

minerals

Fluid inclusions in pyroxenes were two phase rich inclusions with a gas-to-liquid ratio between 0.25 and 0.70 Fluid inclusions in pyroxene are small (5–15 μm), whereas the garnet-hosted inclusions have diameters ranging from 10 to 30 μm (Figure 15) Type I and Type

liquid-II inclusions have been observed in the garnets associated either with the magnetite or pyrrhotite ore However Type III inclusions were observed mainly in the magnetite ore

at Çatak

In garnets from Küreci (KUR 1-4), formed along the contact between granodiorite and limestone, the homogenization temperatures of inclusions (Types I and II) vary from 306.5 to over 600°C The mean of the frequency distribution yield temperatures of 424°C However the homogenization temperatures of inclusions (Types I and II) in the Çatak garnets (CT-12) vary from

227 to over 600°C The mean of the frequency distribution yield temperatures of 473°C (Figure 14a)

The final dissolution of daughter crystals always preceded the final homogenization Halite dissolved at temperatures ranging from 285 to 492°C in garnets from Çatak (EMK-3) Ensuing homogenization to liquid after halite dissolution occurs between 405 to over 600°C.Salinities for Type I and Type II inclusions were, based on final ice melting (T-m ice), computed For Type III inclusions (liquid + vapor + solid) from the Çatak garnets (EMK-3), the salinity was determined from the temperature of dissolution of the halite

Final ice melting temperatures of inclusions in the Çatak garnets (Types I and II in CT-12) range from –2.1

to –18.2°C (Table 5), which correspond to salinities of

3.5–21.1 wt% NaCl equivalent (Potter et al 1978; Bodnar

1993) Final ice melting temperatures of Types I and II inclusions of garnets from Küreci (KUR1-4) range from –20.4 to –69°C (Table 5), which correspond to salinities of

10.4–22.6 wt% NaCl equivalent (Potter et al 1978; Bodnar

1993)

Figure 7 Schematic diagram showing paragenetic relationship

of skarn and ore assemblages of the pyrrhotite-bearing skarns.

Figure 8 Geological section with sample locations illustrating the general setting of the Sakari magnetite skarn.

H

H H H H H H H

H H H H H H

skarn + ore skarn>>ore hornfels

oxidized ore ore

mag>>pyro

rubble

H

H H H

OC-16

OC-19OC-14

OC-22OC-17

OC-1

1

Diopside-dominated pyroxenes in the proximal zone

are represented by a homogenization temperature of 424

to >600°C Inclusions in pyroxene are characterized by a

salinity range of 6.2–10.6 wt% NaCl equivalent (Figure

14a, b)

The first ice-melting temperatures vary from –37 to

–67 °C, indicating the presence of CaCl2 in addition to

NaCl (Shepherd et al 1985; Oakes et al 1990).

Liquid-rich fluid inclusions (Type 1) locally occur

together with vapour-rich inclusions (type 2), suggesting

heterogeneous trapping of a boiling fluid during arsenopyrite-pyrrhotite vein formation in the Çatak skarn (Roedder 1984; Bodnar 1995)

pyrite-8 Geochemistry

Geochemical analyses were performed on different rock types, including the intrusion (n= 11), skarn (n= 10), hornfels (n= 6) and ore facies (n= 8), to characterize the mass transfer during mineralization and different types of alteration Trace and rare earth element (REE)

silicate

d c

Figure 9 Photomicrographs of skarn assemblages from Sakari (a) Replacement of early pyroxene (cpx) by magnetite; (b) textural

relationship between early calc-silicates (garnet chiefly) and ore minerals magnetite (mt) and pyrrhotite (po); (c) epidote (ep) is the most common retrograde mineral in garnet (gt) dominated (gt>cpx) skarn; (d) precipitation of magnetite (mt) and pyrrhotite (po) following the deposition of pyroxene in the main prograde stage; (e, f) the fractures of magnetite and the wall rock are filled by later sulphides,

mainly hexagonal pyrrhotite (po) and chalcopyrite (cpy).

abundances provide an opportunity to investigate the

interaction between the mineralizing fluids and the host

rocks Details of the analytical methods of whole-rock

geochemical analysis are presented in the Appendix Data

for all samples are given in Table 6

8.1 Hornfels

Chondrite-normalized REE patterns of hornfels samples

are shown in Figure 16a Enrichment of LREE over HREE

is obvious, with slightly negative Eu, except in sample

OC1-14, which is a hornfels composed mainly of pyroxene,

amphibole, and plagioclase The positive Eu anomaly

in OC1-14 is significant, with a relatively high Eu/Eu*

value (Eu/Eu*= 2.14) It seems likely that the interaction

of hydrothermal fluids with the plagioclase-rich rock

led to successive enrichment in Eu OC-24 is a hornfels,

containing high proportions of pyroxene and subordinate

feldspar, quartz, amphibole, and chlorite

Tourmaline-bearing metasomatized schist (CT4-3) surrounding

pyrrhotite-dominated skarns has high REE concentrations

The degree of enrichment in this sample is higher in LREE

than in HREE with a negative Eu anomaly Sample CT4-3 shows slightly negative Ce/Ce* (Ce/Ce*= 0.90) and high La/Ybn (La/Ybn= 11.51) ratios, with greater enrichment of

LREE than HREE and a negative Eu anomaly (Eu/Eu*= 0.44) Trace-element data normalized to average crust are plotted in Figure 16b Hornfels samples are enriched in

U, Rb, Tb, Tm, Y and Yb and depleted in Ba, K, Sr, Zr, P and Ti relative to average crust The hornfels samples show similar REE element abundances and patterns to intrusive rocks, although with lesser negative Eu anomalies This could be indicator of the interaction between melt and meta-pelitic rocks during the emplacement of intrusive rocks

8.2 Prograde skarn and ore samples

In the Maden area, endoskarn (KUR1-2) and exoskarn samples KUR1-3, KUR1-4 and KUR1-6 are located with increasing distance from the contact, and exhibit concordant REE patterns reflecting depletion with increasing distance from the pluton towards the recrystallized limestone front (Figure 16c) The same trend in trace elements is also evident in Figure 16d This depletion trend implies that trace and REE were transported by magmatic hydrothermal fluids, although their partition between the minerals was controlled by distribution coefficients between fluids and minerals The REE pattern of KUR1-3 is pronounced with a positive Eu anomaly, which reflects its higher Eu/Eu* ratio (Eu/Eu*= 1.23) The positive Eu anomaly, observed only in KUR1-3, may be related to its zoned garnets that formed by lattice diffusion and growth entrapment processes Garnet-dominated skarn samples (OC-19 and OCT-16) display depletion of LREE and a relative enrichment in heavy REE with a convex-up pattern (Figure 16Ee) Sample OC-19 is a fine-grained skarn sample composed mainly

of garnet, pyroxene, magnetite, and epidote OCT-16 is a coarse-grained skarn sample composed mainly of garnet, pyroxene, amphibole, chlorite, and magnetite This type

of REE distribution in garnets is attributed to garnetites (Whitney & Olmsted 1998) The positive Eu anomaly in the hedenbergite-grossular-epidote-dominant skarn sample (OC-17) is significant with the relatively high Eu/Eu* value (Eu/Eu*= 3.45)

Garnet-bearing samples have relatively high HREE patterns, and garnet appears to account for most of the HREE Due to its larger size (r= 1.26 A), Eu2+ can only be hosted by a nearly pure andradite end-member (Whitney

& Olmsted 1998) Eu3+, transported in retrograde hydrothermal fluids probably producing grossular veinlets, may also account for the positive anomaly (Whitney & Olmsted 1998) OC-17 has grandite garnet (Gr53 An41) reflecting that the positive anomaly is related to the enrichment of hydrothermal fluid in Eu3+ rather than

Eu2+ due to the substitution of Ca by Eu2+

Figure 10 Schematic diagram showing paragenetic relationship

of skarn and ore assemblages of the magnetite bearing skarns.