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Skarn Alteration and Au-Cu Mineralization Associated with Tertiary Granitoids in Northwestern Turkey: Evidence from the Evciler Deposit, Kazda Massif, Turkey

Yeim Yücel Öztürk and Cahit Helvaci

Dokuz Eylül Üniversitesi, Mühendislik Fakültesi, Jeoloji Mühendislii Bölümü, Kaynaklar Kampüsü, 35160 Buca-zmir, Türkey

Corresponding author: e-mail, yesim.yucel{at}deu.edu.tr

The Evciler Au-Cu district is located in the Kazda region of northwestern Anatolia, Turkey. Skarn alteration and Au-Cu mineralization assemblages are related to an elliptical I-type, magnetite series, metaluminous, calc-alkaline body, which has intruded the Kazda Massif. The skarns have an oxidized mineralogy dominated by garnet (Ad₈₅Gr₁₅-Ad₅₀Gr₅₀), hedenbergitic pyroxene (Di₇₀Hd₃₀-Di₂₅Hd₇₅), epidote, amphibole, and chlorite and contain up to 80 percent sulfides (pyrrhotite >> pyrite + chalcopyrite). The massive pyrrhotite-bearing mineralization replaced prograde skarn and marble. At least two paragenetic stages of skarn formation and ore deposition have been recognized: stage I hedenbergitic pyroxene ± garnet ± scapolite ± quartz ± magnetite, and stage II amphibole ± epidote ± chlorite ± quartz ± calcite and pyrrothite + chalcopyrite ± pyrite. Early skarn formation (stage I) was dominated by anhydrous minerals, hedenbergitic pyroxene, and garnet. The hydrous skarn assemblage (stage II) replaced early-formed skarn assemblages. Clinopyroxene is hedenbergite rich, whereas garnet is andraditic. The mineralogy and character of the Evciler skarn is consistent with deposition under oxidized conditions, formation at shallow crustal levels and similar to those of other Cu-Au, Fe-bearing skarn systems. Stable isotope data indicate that magmatic water was involved in the early stage of skarn formation (¹⁸O_H2O= 6.3–10.9) and a mixed magmatic-meteoric water was responsible for the subsequent mineralization (¹⁸O_H2O = –4.6 to +1.0, D_H2O= –30.9 to –17.7).