Abstract:

The Küre volcanogenic massive sulfide deposits lie within the Kastamonu province in the western part of the Pontide tectonic belt of Turkey, and are hosted by ophiolite-related pre-Liassic basaltic sequences. Mineralogical studies of the pyritic massive sulfide deposits of the Küre mining district have shown that the sulfide assemblages, particularly pyrite, have undergone a history of deformation and metamorphism. The Küre volcanogenic massive sulfide deposits show a range of macroscopic and microscopic textures, which are also observed in metamorphosed VMS deposits elsewhere. These textures are cataclastic, annealing and fracture-filling textures which developed in two successive stages; cataclastic texture predominated during main deformational stages, whereas annealing and fracture filling textures predominate during late-deformational stages. Cataclastic texture predominantes in polycrystalline and coarser-grained pyrite. Little or no cataclastic texture is observed in single, fine-grained pyrite crystals. Annealing is characterized by recrystallization of pyrite, while fracture filling is characterized by replacement and infilling of cataclastic fractures in pyrite grains by chalcopyrite. Cataclastic deformation texture is likely to have formed at about 400°C to 500°C and at 1 kb to 3 kb pressures, typical of low-grade and/or greenschist-facies metamorphic conditions, whereas annealing textures dominate at temperatures over 500°C-550°C and at 0.69 kb to 1.7 kb pressures, typical of upper greenschist-/amphibolite-facies metamorphism. Fracture-filling textures, however, should have formed at less than 600°C and less than 500 bars. These temperatures indicate the maximum temperatures that could be reached in such deformation processes. The actual temperatures should be less than these values. The coexistence of at least two or all of the textures in at least one sample from the Küre massive sulfide deposits may indicate that the ore bodies were subjected to a progressive deformation/metamorphic event, ranging from greenschist- to upper greenschist- or even to amphibolite-facies conditions. The imbricate thrust fault and plunging anticlinal/synclinal structures between the Akgöl Formation and the Küre Ophiolite, which postdate the formation of the massive sulfide deposits, may have been the driving mechanism for the development of deformational- and late-deformational textures in the district. Also, it is proposed that many of the copper-bearing minerals may have been remobilized from their original settings to nearby fractures during late deformational stages; this is a possible explanation of why the massive ore tends to be confined to fault planes rather than within altered basalt sequences.

Keywords: