CHROMITE ORE DEPOSITS WITHIN THE HELLENIDE OPHIOLITES: A KEY TO GENETIC PROCESSES AND POST-GENETIC EVOLUTION

Abstract

Chromite ore deposits hosted in the Hellenide ophiolites provide key insights into mantle processes, geodynamic evolution, and post-magmatic modification within the Mesozoic Neo-Tethyan realm. This study synthesizes geological, minero-chemical, and platinum-group elements (PGE) data from well-characterized chromitites hosted in the Pelagonian-Subpelagonian Zone (Vourinos, Pindos, Othrys, Evia), the Vardar Zone (Veria, Vavdos, Skyros), and the Serbo-Macedonian Massif (Gomati, Nea Roda). Chromite compositions are characterized by variable compositions reflected mainly by wide variations in Cr# and Mg#, due to both primary magmatic processes and secondary modifications. Principal Component Analysis (PCA) of major element data identifies three dominant controls on chromite variability. The first principal component (PC1) records Cr–Al and Mg–Fe²⁺ substitutions and captures the primary magmatic signal related to mantle depletion and melt composition. The second principal component (PC2) reflects subsolidus Mg-Fe²⁺ re-equilibration and the third principal component (PC3) records redox variations during metamorphic events.

Pelagonian-Subpelagonian chromitites display the widest compositional range, including both high-Cr, boninitic-like forearc chromitites and high-Al, transitional MOR-SSZ varieties, reflecting variable degrees of mantle depletion and melt-rock interaction. Vardar chromitites retain a primary supra-subduction zone (SSZ) affinity, but commonly record deformation and Fe-Mg re-equilibration and, locally, metasomatic PGE redistribution, particularly in high-strain zones. In contrast, chromitites of the Serbo-Macedonian Massif are strongly affected by amphibolite- to greenschist-facies metamorphism, resulting in systematic Fe³⁺ enrichment and partial to complete modification of primary magmatic signatures. This study demonstrates that PCA provides a robust quantitative framework for distinguishing between magmatic and secondary controls on chromite chemistry. The results highlight a progressive transition from magmatically dominated to metamorphically overprinted systems across the Hellenides, emphasizing the need to carefully consider post-magmatic processes when interpreting chromitite genesis in complex tectonic environments.