Synkinematic skarns and fluid drainage along detachments: The West Cycladic Detachment System on Serifos Island (Cyclades, Greece) and its related mineralization

On the Color and Genesis of Prase (Green Quartz) and Amethyst from the Island of Serifos, Cyclades, Greece

“…The majority of previous studies suggested that the color of the Serifos green quartz was caused by hedenbergite-rich pyroxene inclusions (e.g., [27,31]), and only Hyrsl and Niedermayr [28] reported actinolite, based on XRD analyses, but did not present any analytical data. Our new data suggests that it is indeed amphiboles which are responsible for the typical green color.…”

“…Serifos is occupied by a metamorphic sequence which comprises [38][39][40]: (a) a basal gneiss, mylonitic schists and marbles unit, with a maximum thickness of about 200m, that has been interpreted as member of the CCBU; (b) an intermediate rock unit made of amphibolites and overlying greenschists with rare marble intercalations, occupying the northern part of the Island and containing relics of glaucophane, that are typical of the CBU [41]; (c) and finally, an uppermost unit with marbles, ankeritised protocataclastic shales and minor serpentinite [31]. Contacts between the rock units are marked by tectonic structures (Figure 1), namely the Megalo Livadi and Kavos Kyklopas detachment faults, which belong to the West Cycladic Detachment System, (WCDS, [42]) and are characterized by top-to-the SSW kinematics on the footwalls.…”

“…Contacts between the rock units are marked by tectonic structures (Figure 1), namely the Megalo Livadi and Kavos Kyklopas detachment faults, which belong to the West Cycladic Detachment System, (WCDS, [42]) and are characterized by top-to-the SSW kinematics on the footwalls. [31]). Black squares indicate the study areas of Avessalos (South) and Neroutsika (North).…”

“…A number of skarns have formed close to the granodiorite intrusion [39][40][41]43] and have been long known for their Fe-rich mineralisation, that was exploited until the 1960's. Mines are widespread over the Island and were targeted at magnetite-rich skarn zones or in hematite/limonite±barite orebodies in marbles [31]. These skarns are also the general area where the unique Serifos green quartz, Minerals 2018, 8, 487 5 of 13 mostly known as prase (or prasem), is found ( Figure 2).…”

“…Green quartz is often found in geodes between brecciated, up to tens of meters-sized blocks of skarnified amphibolites [25,26,29,30]. Brecciation of the amphibolites has been caused by the activation of the WCDS and created pathways through which hydrothermal fluids arising from the granodiorite created the widespread skarns on the Island [31].…”