Abstract

The Kassandra mining district of northern Greece contains about 12 Moz Au in porphyry Au-Cu and Au-Ag-Pb-Zn-Cu carbonate replacement deposits that are associated with Oligocene-Miocene intrusions emplaced into polydeformed metamorphic basement rocks belonging to the Permo-Carboniferous to Late Jurassic Kerdilion unit and the Ordovician-Silurian Vertiskos unit. Regional extensional tectonics active since the middle Eocene resulted in the development of widespread normal and transtensional faults, including the Stratoni fault zone that hosts carbonate replacement sulfide orebodies. This structure has been previously interpreted as the tectonic boundary between the Kerdilion and Vertiskos units. Geologic relationships, structural patterns, immobile element geochemistry, and published zircon U-Pb ages suggest that the tectonic boundary between these lithotectonic units is an older structure and not a detachment fault as previously indicated.

Carbonate-hosted replacement orebodies at the Olympias, Madem Lakkos, and Mavres Petres deposits are controlled by the Kassandra fault and Stratoni fault zones. Orebody location and morphology is influenced by a preexisting ductile structural architecture and the interaction of ductile to brittle faults with marble host rocks. Intersection of ductile fabrics and folds with extensional mylonites and synmineral semibrittle shear zones form a linear plunging domain that controls sulfide ore at the Olympias deposit. The Madem Lakkos sulfide orebodies are hosted by marbles located within fold hinges and intersecting semibrittle faults, whereas the Mavres Petres orebody is controlled by lenses of marble entrained within the Stratoni fault zone. Hydrothermal mica 40Ar/39Ar ages indicate that sulfide ore deposition occurred between 24.0 ± 0.6 and 22.6 ± 0.3 Ma, overlapping with late Oligocene magmatism in the district. Kinematic fault-slip data and field relationships suggest that carbonate replacement mineralization within the Stratoni fault zone was initiated toward the end of north-south extension during the late Oligocene, whereas younger Au-bearing quartz-rhodochrosite vein breccias that are spatially related to but crosscut sulfide ores were controlled largely by east-west extension.

The Skouries Au-Cu deposit is hosted by an early Miocene quartz monzonite porphyry stock that postdates the folding of gneiss and schist of the Vertiskos unit. Mineralized veins within the stock and porphyry dikes predominately strike northeast, consistent with the orientation of the Oligo-Miocene igneous belt. Ascent of fertile magmas into the upper crust may have been triggered by a change in the extension direction during the early Miocene. Magmatism during the late Oligocene and early Miocene corresponds to distinct extensional episodes that facilitated polymetallic carbonate replacement and porphyry Au-Cu ore formation within an evolving post-collisional tectonic setting.

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