Yolindi (Biga, Çanakkale) Fe-Cu skarn cevherleşmesinin evrimi: Mineralojik, jeokimyasal ve izotopik yaklaşımlar
Evolution of the Yolindi (Biga, Çanakkale) Fe-Cu skarn deposit: Mineralogical, geochemical and isotopic approaches
Yazar: MUSTAFA KAYA
Danışman: PROF. DR. MUSTAFA KUMRAL ; DOÇ. DR. AMR ABDELNASSER ALİ KHALİL
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı / Jeoloji Mühendisliği Bilim Dalı
Derece: Doktora, 2023
Konu: Jeoloji Mühendisliği = Geological Engineering

Özet:
Yolindi bölgesinde Şaroluk granitoyidi ile ilgili daha önce de jeolojik ve petrolojik araştırmalar yapılmıştır. Ancak, Şaroluk granitoyid sokulumunun cevher oluşturma potansiyeline yönelik yapılmış bir çalışma bulunmamaktadır. Bu çalışmayla bölgedeki skarn cevherleşmesi keşfedilerek, prograd evreden retrograd alterasyonlara kadar skarn evriminin aşamaları incelenmekte ve bulgular daha geniş bir jeolojik, mineralojik ve jeokimyasal çerçeve içinde değerlendirilmektedir. Ayrıca yapılan çalışma, Yolindi cevherleşmesinin evrimsel geçmişini bir ada-yayı ortamındaki kalkalkalin magmatik aktivite ile ilişkili olarak değerlendirmekte ve mineral bileşimlerini ve oluşumunu diğer küresel ve bölgesel Fe-Cu skarn yatakları ile karşılaştırmaktadır. Biga Yarımadası'ndaki Yolindi Fe-Cu skarn yatağı, Şaroluk kuvars monzonit sokulumunun fillit, şist, hornfels, mermer içeren Paleozoyik yaşlı Torasan Formasyonu kayaçlarına intrüzyonu ile oluşmuştur. Skarnlaşma sırasında Şaroluk kuvars monzonit sokulumundan gelen magmatik akışkanlar ile Torasan Formasyonu arasındaki reaksiyonlar demir (Fe) ve bakır (Cu) gibi metallerle ilişkili skarn mineralleri meydana getirmiştir. Başlangıçta bu reaksiyonlar, magnetit ve pirit içeren ojit bakımından zengin piroksenler ve andradit garnet gibi prograd skarn mineralleri oluşturmuştur. Sistem soğudukça, bu ilk mineraller retrograd alterasyona uğrayarak epidot, aktinolit ve klorit gibi minerallerin yanı sıra kalkopirit, bornit, ikincil manyetit ve speküler hematit gibi diğer bakır ve demir minerallerinin oluşumuna yol açmıştır. Skarn oluşumu, Torasan Formasyonu ile temas halindeki Şaroluk granitoid intrüzyonu çevresinde konsantrik ve kontak-metamorfik alterasyon modellerini gösteren farklı mineral toplulukları ile endoskarn ve egzoskarn evrelerine (proksimal, intermediate ve distal zonlar) ayrılmaktadır. Kükürt δ34S izotop değerleri endoskarn zonda +0,57 ‰ VCDT pozitif değerlerinden başlayıp, dış zonlara doğru proksimal ve intermediate ekzoskarn zonda -9,44 ‰ VCDT negatif değerlere kadar ulaşmaktadır. Bu değerler, magmatik, sedimanter ve muhtemelen organik madde dahil olmak üzere çok çeşitli kükürt kaynağına işaret etmektedir. Özellikle endoskarn zonda hidrotermal akışkanların δ34S değerleri magmatik-hidrotermal bir kökene işaret etmektedir. Endoskarn ve proksimal bölge hidrotermal akışkanları hafif bir negatif özellik gösterirken, intermediate bölgede ise hidrotermal akışkanların organik açıdan zengin kaynaklardan ve/veya metamorfik sülfür kaynaklarından güçlü şekilde etkilendiği görülmektedir. Kalsitin karbon ve oksijen izotopik bileşimleri (δ13C ve δ18O), mermer örneklerindeki denizel karbonat özelliklerinden (+1.89 ila +2.23‰ VPDB; +21.61 ila +21.73‰ VSMOW), yüksek sıcaklıktaki magmatik akışkanlar ile mermerin çözünerek dekarbonizasyonun etkilerini yansıtan prograd evrede (-6.0 ila +0.09‰ VPDB; +6.22 ila +18.14‰ VSMOW) ve meteorik su ile karışımın etkilerini gösteren retrograd evrede (-3.8 ila -2.25‰ VPDB; +0.94 ila +3.62‰ VSMOW) azalmış değerlere doğru bir ilerleme göstermektedir. Prograd minerallerdeki sıvı kapanım verilerinden elde edilen yüksek sıcaklıklar (412,20°C'ye kadar) ve tuzluluklar (%26,07 NaCl eşdeğerine kadar), kaynama koşulları altında erken skarn oluşumuna (prograd) işaret etmektedir. Buna karşılık, retrograd evrede gözlenen daha soğuk, seyreltik akışkanların meteorik sularla karışımının arttığını ve ana kayalardaki organik malzemelerle etkileşime girdiğini göstermektedir. Bu da çeşitli kaynak ve süreçleri içeren çok yönlü bir kökene işaret etmektedir. Bu çalışmada, Yolindi bölgesindeki Fe-Cu skarn cevherleşmesinin magmatik, metamorfik ve meteorik akışkanlar arasındaki karmaşık etkileşimlerden kaynaklandığı ve skarn cevherleşmesinin bölgesel metalojenisi için etkileri olan dinamik bir cevher oluşturma ortamını yansıttığı sonucuna varılmıştır. Yolindi Fe-Cu Skarn cevherleşmesinin oluşumunu dört ana aşama etkilemiştir: metamorfik-bimetasomatik, prograd evre, retrograd evre ve ilerleyen süreçte, metasomatizma sonrası bir süperjen evre olan ayrışma ve oksidasyon evresi tanımlanmıştır. Andradit-grossular geçişi gibi mineralojik değişimler, meteorik akışkanların eklenmesine bağlı olarak değişen hidrotermal akışkan bileşimlerini ve özelliklerini yansıtmaktadır. Yolindi Fe-Cu Skarn cevherleşmesinin mineral bileşimleri, Dünya'da bilinen skarn yatakları ve Türkiye'deki skarn yatakları (örneğin, Ayazmant Fe-Cu ve Evciler Cu-Au skarn yatakları) ile uyumludur. Yolindi Fe-Cu Skarn cevherleşmesi, magmatik kökenli cevher içeren akışkanlarla ilişkili olarak ada yayı ortamında gelişmiştir.

Abstract:
Previous geological and petrological studies have been carried out on the Şaroluk granitoid and its country rocks in the Yolindi area by many authors. However, these studies did not specifically focus on investigating the origin of the Cu-Fe skarn mineralization associated with this granitoid. Therefore, the current thesis tried to investigate the genesis and evolution of this Cu-Fe skarn mineralization in the region. It especially studies the relationship between the Şaroluk granitoid intrusion and the surrounding Torasan Formation rocks. Furthermore, it discusses the metasomatic processes responsible for the formation of skarn mineralogy, emphasizing the essential role of magmatic fluids in the evolution, alteration, and interaction of skarn minerals with copper and iron. Moreover, it aims to construct and clarify various stages of skarn evolution, including both prograde and retrograde alterations. Furthermore, this thesis also aims to evaluate the physiochemical conditions and fluid within the examined mineralization. To do this, an exhaustive investigation of geological and mineralogical data will be conducted, along with the assessment of sulfur isotopes (δ34S), carbon isotopes (δ13C), and oxygen isotopes (δ18O) in sulfide and calcite minerals, respectively. Furthermore, the investigation will include analyzing fluid inclusion data for several minerals, including andradite, quartz, and calcite. A geochemical study was undertaken to investigate the chemical interactions between the rocks hosting hydrothermal ore fluids, with a special emphasis on the alterations induced by the hydrothermal process. An analysis of skarn, alteration, and ore minerals is conducted to determine the specific pressure and temperature conditions during the formation of the ore. Moreover, it aims to examine the mineral composition and origin of the Yolindi deposit in relation to other global and local Cu-Fe skarn deposits. It also evaluates the evolution of these deposits over time in relation to magmatic activity, particularly in an island-arc environment. 
The Yolindi area is situated in Çanakkale province, Biga Peninsula, NW Turkey. The Paleozoic Kalabak Group and Triassic Karakaya Complex, which were intruded by Early Miocene Şaroluk granitoids, constitute the Yolindi area. The Kalabak Group comprises the basement of the Sakarya Zone, a tectonic unit with the Torasan Formation at the base and the Sazak Formation at the top, subsequently invaded by Yolinidi metagranodiorite. In the western study area, the Lower Paleozoic Torasan Formation (Pzt) lies near Yolindi village, Bıçkı, and Baltaoluk hill. Actinolite hornfels, metasandstone, metasiltstone, phyllites, muscovite-, biotite-, talc-, tremolite-, chlorite-schists, and related tuffs made up much of this Formation. Serpentine peridotites (Pzts) and marble block and lens members are in the phyllites. The phyllite comprises muscovite, biotite, quartz, and opaque minerals. Quartz, actinolite, clinozoisite, clinopyroxene, and opaque minerals are the mineral compositions of the actinolite hornfels. While antigorite, chlorite, clinopyroxene, and a few opaque minerals represent the constituents of the serpentinite lenses. Calcite-based marble and recrystallized limestone have a delicate texture. The early Middle Devonian Yolindi metagranitoids (Pzy) have been identified around the Yolindi village. Biotite gneiss and metagranodiorite are included. Biotite gneiss is composed of quartz, sericitized plagioclase, biotite, and opaque minerals. While the metagranodiorite consists of sericitized plagioclase, quartz, biotite, and opaque minerals. Near Inova and Tahtali, the Triassic Karakaya Complex (Trkk) lies in the central and western parts of the study area. It contains marble, metasandstone, phyllite, metavolcanics, and serpentinites. The Şaroluk granitoid (Tmş) is a 20 km2 east-west elliptical pluton. The Şaroluk pluton was formed by Early Miocene magmatic activity. A hornfels zone has formed in the Torasan Formation on the western margin of the Şaroluk intrusion. The Şaroluk pluton has primarily quartz monzonite with minor granodiorite. The quartz monzonite contains mainly biotite, tremolite, actinolite, K-feldspar, quartz, and biotite with subordinate tremolite. Plagioclase (50%–70%), quartz (20%–30%), microperthite (5%–15%), hornblende, biotite, minor amounts of pyroxene, and opaque minerals are the mineral compositions of the granodiorite. The Hallaçlar Formation (Tmh) is located southwest of the study area, around the Beyoluk village, Bayındırlık Hill, Koca Hill, and Deniz Hill. It originated as a result of volcanic activity that occurred during the Late Oligocene and Early Miocene periods. It includes pyroclastic, felsic tuffs, and rhyodacite and porphyritic andesite. The porphyritic andesite consists essentially of hornblende, biotite, and plagioclase phenocrysts embedded in fine-grained microcrystalline plagioclase laths, quartz, and opaque minerals.
The zonal alteration patterns observed in the Yolindi Cu-Fe (±Zn ± Pb) skarn mineralization occurred in concentric or perpendicular mannar to the contact between the Şaroluk granitoid intrusion and the Torasan Formation, as well as carbonate-rich rock or limestone. They primarily consist of endoskarn and exoskarn zones, with the exoskarns being further divided into proximal, intermediate, and distal zones based on their proximity to the intrusive body. Şaroluk quartz monzonite bleached at the Torasan Formation-Şaroluk intrusion boundary forming the endoskarn zone at the outermost parts of the Şaroluk intrusive body. It is particularly noticeable near Maden Deresi and İmameğreği Sırtı. Skarnized granitoids, which include andradite and garnet with epidote and sericite formation during metasomatism. In Maden Deresi, magnetite-bearing granodiorite undergoes minimal alterations increasing nearer the contact zone. The magnetite-bearing endoskarn contains andradite, epidote, magnetite, and goethite. The İmameğreği Sırtı area is known for its magnetite- and pyrite-bearing granodiorite, with quartz, plagioclase, microperthite, biotite, diopside, actinolite, sphene, and hematite. Conversely, exoskarns surrounding the Şaroluk granitoid body in Torasan formation often include magnetite, pyrite, epidote, scapolite, garnet, pyroxene, chalcopyrite, bornite, hematite, and sometimes sphalerite and galena. These minerals are distributed in clear patterns within the exoskarns, forming proximal, intermediate, and distal subzones.
The ore mineralogy includes magnetite, pyrite, chalcopyrite, specular hematite, galena, sphalerite, cerussite, malachite, and goethite. Magnetite and pyrite in association with andradite and augite minerals within the endoskarn and proximal prograde exoskarn zones. Chalcopyrite dominates the copper-iron sulfide mineral in the proximal retrograde exoskarn zone northwest of Sarıot Deresi and the intermediate zone. Pyrite often develops in the intermediate exoskarn zones, along with chalcopyrite, hematite, and bornite. Specular hematite forms with chalcopyrite and pyrite in the exoskarn intermediate zone. Large, distinct subhedral light gray crystals of galena mix with sphalerite and transform into cerussite. Paragenesis inquiries of Yolindi Cu-Fe skarn mineralization identified three mineralization phases based on metamorphic, alteration, and ore mineral relationships. During the prograde stage, magnetite and pyrite occurred with medium- to coarse-grained Fe-rich anhydrous calc-silicate minerals (andradite and augite). Actinolite, epidote, scapolite, calcite, and chlorite pseudomorphs after garnet and pyroxene imply a retrograde stage at lower temperatures and pressures. At this stage, andradite-grossular intergrowth is associated with hedenbergite. These minerals commonly form with chalcopyrite, pyrite, specular hematite, galena, and sphalerite. Malachite and cerussite are supergene stage characteristics. This illustrates metals migrating and leaching from surrounding areas where primary metal sulfides break down and form carbonates when pH and redox conditions change.
The geochemistry of the Yolindi metagranodiorites and Şaroluk granitoids indicates that they belong to the granite and granodiorite and quartz monzonite and monzonite fields, respectively, with calc-alkaline affinities and primarily following compressional suite trends. Most Yolindi metagranodiorites are S-type granitic suites, whereas Şaroluk granitoids are I-type. The magnetite series includes volcanic-arc granite (VAG) and post-collision granite. The chondrite-normalized REE patterns show that they developed during differentiation due to their high LREE content and Eu-negative anomalies. The primordial mantle-normalized immobile element profiles of the investigated granitoid rocks show depletion in Ba, Nb, Sr, P, Zr, Eu, and Ti relative to Th-U, K, and La-Pb, supporting subduction-associated petrogenesis. These rocks' upper continental crust (UCC)-normalized REE pattern is flat, which matches UCC compositions. On the other hand, the geochemical characteristics revealed that the unaltered Torasan Formation, which includes metatuffs, metasediments, and schists, originates from several sources, primarily quartz diorite, granodiorite, and granitic, with little basalt and andesite with acidic and intermediate characteristics from upper continental crust metavolcanic tuffs, metagreywackes, and arkosic sands. The majority of them were derived from ancient sedimentary rocks originating from extensively weathered mafic and felsic terrains within a combination of felsic/basic and relatively less andesitic continental magmatic arc, resembling the characteristic composition of the upper continental crust.
The alteration geochemistry shows that the endoskarn, proximal, intermediate, and distal skarn zones show lower values in the alteration index (AI) and display clustering and sifting towards the calcite and epidote fields (propylitic alteration). This indicates that these alteration zones were associated with the removal of alkali elements and enrichment of CaO, except for certain samples from the endoskarn and distal zones, which exhibit advanced argillic signatures due to sericite, kaolinite, and pyrophyllite alteration.
Garnet, clinopyroxene, scapolite, plagioclase, epidote, biotite, chlorite, sericite, calcic amphibole, carbonate (calcite and cerussite), magnetite, hematite, and sulfide (pyrite, chalcopyrite, and galena) were analyzed with an electron microprobe from Yolindi skarn zonations. This endoskarn zone garnet is unzoned andradite that was partially transformed to epidote, with high SiO2, FeO, and CaO and low Al2O3. Mostly andradite, its composition is Adr79Grs13Sps0Alm0 to Adr86Grs19Sps3Alm1. The proximal exoskarn zone garnet is zoned andradite in the prograde subzone but intergrows from Fe-rich to Al-rich in the retrograde subzone, generating compositional change and oscillatory zoning. The Adr96Alm3 proximal prograde zone andradite have higher SiO2, FeO, and CaO. However, garnet from the proximal retrograde zone showed andradite-grossular intergrowth from Adr77Grs20Alm1 (Fe-rich) in its core to Adr59Grs39Alm1 (Al-rich) in its rim. However, the intermediate zone garnet is fully andradite to andradite-grossular intergrowth zoning with Adr89Grs11 and Adr49Grs41Alm9. Magmatic garnet (Type D) comes from metasomatic rocks (e.g., skarns), with a little from amphibolite-facies metasedimentary rocks (Type Bii). The garnet classification is comparable with garnet from other Cu-Fe skarn deposits globally, with some Zn. The clinopyroxene minerals from the various skarn zones are augite with a range of En50.6–62.0Fs12.1–23.2Wo24.5–28.4 and En44.8–47.2Fs25.8–28.5Wo25.2–26.9 and Di65.5–78.7Hd15.4–31.1Jhn0.8–7.1 and Di58.2–60.0Hd32.8–37.1Jhn3.6–7.1 for the endoskarn and proximal exoskarn zones, respectively, while they are hedenbergit. Higher diopside and hedenbergite concentrations make the investigated clinopyroxenes consistent with those from other Cu-Fe skarn deposits. Scapolite formed in association with hedenbergite in the exoskarn intermediate zone. The EPMA data shows that the scapolite is a late, Cl-rich scapolite with averages of 33.3 and 2.96 wt.% for Me and Cl, respectively. Epidote was formed by the subsequent replacement of garnet in endoskarn and exoskarn zones that are close to and between garnet, pyroxene, and calcite. The EPMA data obtained from the epidote in this study area was categorized as clinozoisite. The EPMA of chlorite minerals reveals that they are mostly Fe-chlorite (chamosite), except for a few proximal chlorite minerals that are Mg-chlorite (clinochlore). The estimated formation temperatures for these chlorite types decreased from proximal (T = 286 °C) to distal (T = 152 °C) throughout the intermediate zone (T = 179 °C). An analysis was conducted on the chemical compositions of amphibole found throughout several skarn zones within the Yolindi area, which are rich in magnesium and have compositions dominated by actinolite. The FeO concentrations of endoskarn, proximal, and intermediate magnetites range from 92.66% to 95.48% (average 94.53%), 90.07% to 96.72% (average 93.77%), and 91.92% to 93.84% (average 92.99%), respectively. These magnetites also contain lower levels of SiO2 and Al2O3. The proximal and intermediate magnetites show an affinity for hydrothermal conditions, primarily occurring in skarn and contact metasomatic areas, whereas the endoskarn magnetite is associated with magmatic processes.
The fluid inclusions formed in prograde minerals under fluid boiling conditions display elevated temperatures, reaching a maximum of 412°C, and salinities of up to 26 wt.% NaCl equivalent. In contrast, the fluid inclusions were found in minerals from the retrograde zone that formed as a result of fluid mixing and had lower temperatures, averaging at 318 °C, and salinities averaging at 4.9 wt.% NaCl equivalent.  This suggests that cooler, more diluted fluids combine with meteoric waters and come into contact with organic matter in nearby rocks. This implies a complex genesis that encompasses several sources and processes.
The sulfur isotopes (δ34S) of sulfides found in the endoskarn (+0.27 to +0.57‰VCDT) and intermediate exoskarn (−9.44 to −5.46‰VCDT) zones suggest a variety of sulfur sources, such as magmatic, sedimentary, and maybe organic materials. The δ34S values observed in hydrothermal fluids indicate that they originate from a magmatic-hydrothermal source. The fluids from the endoskarn and proximal zones have a somewhat negative signature, while the fluids from the intermediate zone show a significant effect from organic-rich or metamorphic sulfur reservoirs.
The carbon and oxygen isotopic compositions (δ13C and δ18O) of calcite in the marble samples show a transition from marine carbonate characteristics (+1.89 to +2.23‰VPDB; +21.61 to +21.73‰VSMOW) to lower values in the prograde skarns (-6.0 to +0.09‰VPDB; +6.22 to +18.14‰VSMOW) and retrograde skarns (-3.8 to −2.25‰VPDB; +0.94 to +3.62‰VSMOW). This indicates that the samples interacted with high-temperature magmatic fluids and a mixture of meteoric water.
The genetic relationship between Cu-Fe skarn deposits and magmatic activity may apply to other skarn deposits worldwide, including those in the Biga Peninsula in northern Turkey. EPMA data show that garnet is mostly magmatic garnet (Type D), which comes from metasomatic rocks like skarns. The Ayazmant Fe-Cu skarn of Turkey, the Ahar Fe-Cu skarn of Iran, and the Kamaish Fe skarn of Japan are mostly compatible with garnet from other worldwide Cu-Fe skarn deposits, with a little Zn. The investigated clinopyroxenes are comparable with those from the Ayazmant Fe-Cu skarn in Turkey, the Evciler Cu-Au skarn in Turkey, and other Cu-Fe deposits globally. Furthermore, the investigated samples of Şaroluk quartz monzonite rocks have a relationship to the Yolindi Fe-Cu skarn plot. The Şaroluk quartz monzonite, a metaluminous I-type granitoid with higher A/NK and lower A/CNK values, is found near Cu and Zn skarns and Evciler Fe-skarn granitoids. In addition, its samples align with Fe-, Cu-, and Au-skarn granitoids, similar to Evciler Au-Cu granitoids. Also, they investigated in VAG and Syn-COLG, near Cu- and Fe-skarns, show a similar pattern to Evciler Au-Cu granitoids, and Ahar Fe-Cu granitoids. As seen above, the island-arc setting is perfect for Yolindi Cu-Fe skarn deposits and their magmatic ore solution.
Hence, the study results establish that the skarn mineralization in the Yolindi region occurred via the intricate interplay of magmatic, metamorphic, and meteoric fluids, indicating a dynamic environment for the formation of ore, which has significant implications for the broader understanding of Cu-Fe skarn deposits in the region.