Structural Architecture of the Cenozoic Kallianos (Post-?)Orogenic Vein-Hosted Au-Ag-Te Deposit and Its Relationship to the North Cycladic Detachment System, Greece

Abstract

The Kallianos Au-Ag-Te deposit is a Cenozoic orogenic-style deposit on Evia, hosted in the Cycladic Blueschist Unit. Integrated field observations and isotopic data illustrate a connection between the structural architecture that hosts mineralization in the deposit and the regional stress field associated with a crustal-scale detachment, the North Cycladic Detachment System, implying a first-order paragenetic relationship to post-orogenic extension. Mineralized and barren veins occur alongside parallel faults and joints in two distinct orientations, each locally defining conjugate or en-echelon sets. Younger sub-vertical tension gash sets (V₂, V₃) cross-cut older transposed and boudinaged mineralized veins (V₁). Sulfide mineralization is hosted in steeply dipping cm-scale qz ± cal ± ab V₃ veins. Structural relationships show cross-cutting of NW-striking V₂ by NNW-striking V₃ veins. The latter two vein sets opened orthogonal to the NE-trending stretching lineations, associated with brittle-ductile shear bands indicating top-NE kinematics, underscoring their relationship to crustal extension accommodated by the detachment system. Carbon-Oxygen isotope data from vein calcite (δ¹³C: −3.31–0.40‰ and δ¹⁸O: 14.43–20.78‰) reflect fluid mixing with the graphite-bearing wall rock. White mica ⁴⁰Ar/³⁹Ar and in situ ⁸⁷Rb/⁸⁷Sr geochronology suggest that the host rock accommodated greenschist facies deformation between c. 20–31 Ma, whereas hydrothermal mica in vein haloes indicates fluidization and vein sealing at c. 21–26 Ma. Zircon (U-Th)/He dates reveal that the rocks cooled below ∼200°C at c. 11–14 Ma, corresponding to the exhumation of the deposit into the brittle crust. A comprehensive study of this younger, mostly undeformed post-orogenic deposit can help elucidate the tectonic setting of older, polydeformed orogenic gold deposits.