Hahn, Andreas (2014) Nature, timing and geodynamic context of polymetallic mineralisation in the Kassandra mining district, North Greece. (PhD thesis), Kingston University, .
Abstract
The Kassandra mining district in Chalkidiki is an important producer of base and precious metals in northern Greece. The mining district is comprised of two major Pb-Zn (Ag [plus or minus] Au) carbonate-replacement deposits at Olympias and Mavres Petres with total mineable reserves of 0.7 Mt Pb, 0.9 Mt Zn, 64 Moz Ag and 4.1 Moz Au. Skouries is a Cu-Au porphyry resource under development with reserves of 3.6 Moz Au and 0.8 Mt Cu. Despite available data, the geodynamic background of the polymetallic district mineralisation is unknown in the context of regional tectono-magmatic evolution. The scope of this PhD project was to develop an over arching ore-genetic model for the diverse mineralisation styles in the Kassandra mining district. The polymetallic zonation and spatial distribution of diverse mineralisation styles in the study area is characteristic for an intrusion-centred ore system. Subeconomic to economically important Cu-Au porphyry copper, Cu-skarn, Pb-Zn (Ag [plus or minus] Au) carbonate-replacement and basement-hosted Fe-Pb ([plus or minus] As) sub-epithermal vein mineralisation between Olympias, Mavres Petres, Madem Lakkos, Stratoni-Fisoka and Skouries represent the proximal to distal parts of a fault-controlled magmatic-hydrothermal system. Fluid inclusion and stable isotope data provided by previous authors identified magmatic and evolved meteoric-hydrothermal fluids in the mineralisation system. New He and S stable isotope data support the involvement of a magmatic component as important metallogenic source for metals, ligands, fluids and heat. Spatially and genetically related to the mineralisation are Oligocene-Miocene stocks and dykes of granite, granodiorite diorite, diorite-gabbro and subordinate gabbro. U-Pb zircon and [sup]40Ar-[sup]39Ar mica ages constrain the mineralisation-related calc-alkaline, medium-K to shoshonitic magmatism to a short-lived cycle between 29 Ma and 20 Ma. A late Oligocene [sup]187Re-[sup]187Os isochron age of 26.1 [plus or minus] 5.3 Ma for ore-related arsenopyrite from the Olympias deposits provides a robust in-situ formation age for the carbonate-replacement mineralisation in the district. Two [sup]40Ar-[sup]39Ar biotite ages of 26.3 [plus or minus] 0.3 Ma and 19.9 [plus or minus] 0.2 Ma date the porphyry-style mineralisation-alteration at Stratoni-Fisoka and the economically important Skouries Cu-Au porphyry resource. Magmatism and magmatic-hydrothermal mineralisation in the district were coeval with a phase of post-collisional extension in the North Aegean region. Eocene-Miocene slab roll-back initiated orogen-scale lithospheric stretching, crustal thinning and asthenospheric upwelling which elevated the regional heat gradient. Heat transmission into lower structural levels of the Rhodope nappe pile started and maintained hydrothermal fluid circulation which led to the formation of base metal rich-deposits. Metamorphic and protolith ages of host and country rocks allocate the district mineralisation to the middle to upper tectono-stratigraphic crustal levels. Here, on the flank of the Southern Rhodope core complex, the heat flux was not high enough to initiate large-scale fluid flow. Instead, synetensional partial melting at mid to lower crustal levels, involving fertile and hydrous cumulates in the subduction-modified sub-continental lithospheric mantle, generated hydrous melts with subduction-type chemical signatures that were emplaced in the Kassandra mining district in the magmatic arc above the retreating slab.
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