Ore Mineral Textures of Late Cretaceous Volcanogenic Massive Sulfide Deposits of Turkey: Proposed Paragenetic Sequence

Most of the massive sulfide deposits (VMS) occurring from Precambrian to Cenozoic throughout the world have been subsequently metamorphosed at various grades. Thus, all the original textures have been either completely destroyed or strongly modified. However, there are a very few examples, rather younger deposits such as late Cretaceous Turkish VMS deposits and Miocene Kuroko deposits of Japan in which representative and original ore textures are preserved. The Turkish massive sulfide deposits are mainly Cu–Zn–Pb type and entirely hosted by Late Cretaceous felsic volcanic rocks within a paleoarc geotectonic setting.

Major ore minerals are base metal sulfides (pyrite, chalcopyrite, bornite, chalcocite, covellite, sphalerite, and galena) and sulfosalts along with quartz, barite, and calcite gangue. In general, dissemination and veinlet textures are extremely abundant in the stockwork and siliceous ore zones that mainly form the base of the massive ore bodies and around the vent through which the ore-forming fluids traversed. In the massive ore, particularly in the central zone of the lenses, fine-grained massive sulfide minerals show a wide variety of replacement and colloform textures. In the lateral zones, clastic or fragmental ore textures may be present if the deposit has undergone a slumping. In the case of cone-shaped deposits, the brecciated ore textures tend to be dominant in the central part of the lens. Most of the minerals are very fine grained, and the larger grains of the major minerals are in the order of 100–300 μm in size, but most of the minor and trace minerals are much smaller, typically in the order of 1–20 μm in across. Most of the minerals are anhedral with the exception of pyrite, quartz, and barite that commonly occur as euhedral to subhedral crystals.

Four major mineralization stages have been determined at the regional scale. First-stage minerals are two generations of pyrite and chalcopyrite followed by the second-stage minerals including sphalerite, galena, and sulfosalts (mainly tennantite and subordinate tetrahedrite). In the third stage, second generation of chalcopyrite occurs replacing all the earlier phases. This stage is absent in black ore dominating deposits. Bornite prevails in the last stage (aka supergene enrichment) along with chalcocite and covellite, which replaces all the other phases including gangue minerals.