IRON-OXIDE MINERALIZATION OF SESI, KOROPI (S. HYMITTOS, GREECE): MINERALIZATION WITHIN A DETACHMENT ZONE

Abstract

Small occurrences of iron-oxide deposits at Sesi-Koropi in S. Hymittos, are hosted by an extensional brittle detachment zone between carbonate rocks of "Vari-Kirou Pira" and "Hymittos" units. Another low-angle fault separates a heterogeneous formation of schists, containing meta-ophiolitic blocks ("Lavrion" Unit), which is cut by high-angle normal faults that root in the detachment zone, reducing the total structural thickness of "Hymittos" marbles and bringing in contact the meta-ophiolitc lithologies with the "Vari-Kirou Pira" dolomites. Three mine caves were found along the detachment zone indicating that these iron deposits were possibly mined on a very small scale in the past. The mineralization is developed in a cataclastic zone a few meters thick (3-5m), forming thin rusty black encrustations and larger zones of alteration with a reddish to yellow brown hue. Scanning Electron Microscope (SEM) mineralogical study of the iron-ore deposit indicated that hematite is the primary iron-oxide mineral extensively replaced by goethite. Goethite appears with the typical colloidal form within voids showing typical open-space filling type microstructures. According to field evidence and the tectonic macro-structure of the area, the mineralization is associated with hydrothermal fluid circulation along the brittle detachment zone between meta-ophiolitic lithologies and carbonate rocks. Similar type iron-oxides mineralization in cataclastic zones were observed along other detachment zones in northern and southeastern Hymittos Mt. and further south towards Lavrion. This suggests that this type of mineralization is not local but has a broader development and regional implications for the tectonic evolution of the central and SE Attica