Genesis of filamentary pyrite associated with calcite crystals

The calcite of the hydrothermal Surneshko Kladenche copper vein deposit from the Rossen ore field, Bulgaria, sometimes encloses peculiar filamentary pyrite crystals. Three successive calcite generations were observed belonging to a low-temperature (<235 degrees C) carbonate paragenesis formed in open cavities of the ore veins after the main chalcopyrite mineralisation. three generations of pyrite crystals are associated with these calcite crystals: pyrite 1, with [001] elongated columnar crystals which crystallised in open space; pyrite 2, in groups of long (up to 10 mm) sub-parallel tortuous filaments of varying thickness (3-20 mu m) which are oriented nearly perpendicular to the surfaces of a transient w{3145} scalenohedral calcite crystal zone; and pyrite 3, made of slightly elongated small crystals, located in the outermost nu {2131} zone of the same scalenohedral calcite crystals. The columnar pyrite 1 is formed by subsequent thickening of thin straight whiskers rapidly grown under diffusional regime, whereas the filamentary pyrite 2 and 3 grew contemporaneously with the enclosing calcite crystal.