Deformation of stibnites and pyrites in the Madsan antimony deposit (NiÛde, Turkey): Implications for pressure-temperature conditions of local deformation

Abstract: The Madsan antimony deposit at the southeastern part of the Niğde province (south-central Turkey) includes a series of epithermal veins hosted by marbles and gneisses. The veins have a simple mineralogy of quartz, calcite, stibnite and pyrite as major constituents, and cinnabar occurs in trace amounts. The deposit experienced a progressive deformation evidenced by a set of textures developed especially in stibnite and pyrite. These are pressure lamellae and annealing as the main textures, and curvature, off-set of pressure lamellae and fracture filling as the textures of minor importance. These were developed in three successive deformation phases. Pressure lamellae represent the first stage of deformation in the region, while the second stage of deformation is represented by curved pressure lamellae and annealing texture, and the third stage of deformation is characterised by truncation and offset of pressure lamellae. The deformations probably occurred at temperatures reaching 180°C and at pressures about 0.2 MPa. Geological evidence supports that the first phase of deformation is explained by the southward thrusting of the Niğde Massif over the Ulukışla Basin. The second phase of deformation is due to an increase in internal compression within the stibnites after the firs