Supervisors info:
Dimitrios Kostopoulos, Assistant Professor, School of Sciences Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens
Original Title:
Calamine-type (hemimorphite/smithsonite) zinc mineralization, southern Siphnos Island, Cycladic Archipelago, Aegean Sea, Greece: a possible source of ancient gold
Summary:
The island of Siphnos belongs to the Cycladic Archipelago in the southern Aegean Sea, Greece. In the ancient texts it has been recorded that the wealth of the island, in the 6th century BC, came from the gold and silver mines. In the island of Siphnos, two types of mineralization have been recognized: a carbonate-hosted Ag-bearing Pb mineralization in the central part, and a schist/gneiss-hosted Au mineralization in the southern part. In the present thesis, special emphasis was placed on reported Au-bearing localities from southern Siphnos. Careful mapping and sampling complemented by optical and scanning electron microscopy and mineral chemical analyses on selected samples revealed the presence, for the first time, of calamine-type Zn mineralization. The main site of this type of mineralization is an old zinc mine at Aghios Ioannis locality, some 400m SW of Faros village, that was operated by Kapsalos (Κάψαλος) mining company between 1903 and 1908. The mine is located at the very contact between marble and schist. Mineralization postdates exhumation and retrogression of the Cycladic Blueschist Unit as it is partially hosted by greenschist-facies rocks with relics of glaucophane. The main ore minerals are hemimorphite [Zn4(Si2O7)(OH)2•H2O] and smithsonite (ZnCO3), collectively known as calamine; pyrite, sphalerite and galena, along with chalcocite and covellite were also recognized macroscopically. Calamine has been historically mined from the upper parts of zinc and lead ores. This type of mineralization is interpreted as the result of oxidation of primary sulphide deposits at depth, remobilization and redeposition into dissolutions vugs (i.e. cavities) and karst during water table oscillations.
The Siphnos calamine deposits are very similar to those of Thassos (e.g. Marlou locality) where the ore-bearing horizons appear in carbonate rocks and in schists, and define two different types of deposit: a synsedimentary deposit and a younger karst-filling type. The Au mineralization of Thassos has been related to porphyry-, epithermal- and intrusion-related systems. Although no Cenozoic igneous intrusions have been identified on Siphnos, it is proposed that such bodies must be sought at depth and are responsible for the widespread mineralization seen on the island.
