The Aegean island of Serifos is located about 100 km southeast of Athens and belongs tectonically to the Cycladic Blueschist Unit. Together with Kea, Kithnos, Sifnos, Milos, Folegandros and Sikinos, Serifos is part of the Western Cyclades (Figure 1). The geology of Serifos is largely dominated by an I-type granodiorite pluton occupying the central and southeastern part of the island (Ballindas, 1906; Marinos, 1951). This pluton has intruded higher grade crystalline rocks including gneisses as well as amphibolites that typically alternate with orthogneisses and various types of marbles. Greenschists intercalated with marbles are present in the northern, northwestern and western parts of the island of Serifos (Figure 2).
Serifos is well-known as an example of skarn and ore deposit formation associated with spectacular gem-quality mineralization that has attracted the attention of mineral collectors for decades. Since ancient times, the chief source of wealth on Serifos has been its iron ore (mainly magnetite, hematite and limonite). Although traces of old mines have been destroyed almost completely by mining activities during the 19th and 20th century, the mining history can be reconstructed (with major interruptions) over nearly 3000 years up to closure around 1950. Mining and smelting activities of copper can be traced back probably for even more than 4000 years (Ross, 1840; Philaniotou, 2004).
Earlier workers (e.g. Marinos, 1951) assigned the higher metamorphic grade of the rocks around the intrusive contact as well the skarn and ore deposit formation to contact metamorphism and fluid metasomatism, respectively, that have been induced by the Serifos granodiorite. Based on an extensive study of the paragenetic relations in the Serifos rocks, Salemink (1985) presented a simplified map of contact metamorphic mineral isograds and revealed the physical conditions of skarn and ore deposit formation. According to his results, skarn and ore deposit formation is due to metasomatic and hydrothermal fluid activity that took place during cooling of the granodiorite at high crustal levels. The most important succession of skarn parageneses formed by replacement of silicate rocks during cooling comprises typically (1) andradite-rich garnet + hedenbergite +/- magnetite at c. 600°C (2) andradite-rich garnet + actinolite around 500°C and epidote + actinolite at 300-400°C (Salemink, 1985).
Based on Rb/Sr systematics, Altherr et al. (1982) and Henjes-Kunst et al. (1988) constrained the timing of intrusion on Serifos to between 9.5 and 8.0 Ma. Apatite fission track-ages and model calculations suggest rapid cooling of the granodiorite of more than 50°C/Ma between 8.6 and 6 Ma (Hejl et al., 2002). It should be noted that earlier workers have considered the Serifos granodiorite as a post-tectonically intruded, completely undeformed pluton. Boronkay and Doutsos (1994) however, concluded that the Serifos granodiorite is syn-tectonic with a regional transpressional event that took place under brittle / ductile conditions.