Metamorphic hosted Au-Sb mineralizations in the Nigde Massif (SE Çamardı Region), Central Anatolia: field and ore microscopy studies

The Niğde Massif is a metamorphic core complex located at the southernmost of the Central Anatolian Crystalline Complex (CACC) and is productive in terms of metamorphic-hosted Au-Sb, Au-As mineralization. It is bordered by the Ecemiş fault zone to the east and the Celaller thrust to the south. South-to-north lower-grade metamorphosed units cover ductile deformed high-temperature metamorphic levels on the massif. The massif is mostly composed of the Upper Devonian Gümüşler Formation, Carboniferous-Lower Permian Kaleboynu Formation, and Mesozoic Aşıgediği Formation, which occur unconformably. The Üçkapılı Granodiorite and Sineksizyayla Metagabbro in the Upper Cretaceous cut metamorphics, while post-Paleocene sedimentary deposits in the south and Neogene volcanic deposits in the north cover the entire sequence. Gümüşler, Kaleboynu, and Aşıgediği formations contain gneiss, schist, amphibolite, marble and quartzite units. This study examines the Çamardı region in the southeastern part of the Niğde Massif and the Au-As and Au-Sb mineralizations in this region. In the Çamardı Region, thrusted Gümüşler Formation over the younger Kaleboynu and Aşıgediği metamorphics are in NE-SW direction. This thrust forms the sub-formation which is known as SE Gümüşler, and the average dip- dip direction of the metamorphics forming the base of this formation has been measured as 150/40. Gold mineralization in ductile cataclastic breccia and schists is related with pyrite-arsenopyrite mineralizations. However, gold is related with siliceous-rich matrix with well-developed stibnite crystals in marble-schist contacts at the upper levels. W-E and NW-SE faults have been identified; it has been determined that the NW-SE faults generally intersect the W-E faults. These fault zones may be transfer zones for metamorphic-derived fluids to generate Au-As cataclastic breccias in deep cataclastic zones and Au-Sb mineralized brittle silica-rich breccia in marble-schist contacts at higher levels. It is considered that the Üçkapılı granodiorite and associated aplitic dikes intruding into the schists cut by NW-SE faults in the southwest of the field play a role in the transport and remobilization of Au-As-Sb mineralization observed both within the schists and in the marble-schist contacts. Gold values in rock samples in the field ranged from 0.3-6.7 ppm, while antimony values ranged from %0.3- 1. arsenic values ranged from %0.1-1 in gold-antimony rich samples. In polished sections, gold, arsenopyrite, stibnite, realgar, and marcasite are identified as ore minerals; and quartz, sericite, and rutile as gangue minerals. Gold grains generally range in size from 30-100 µm and are mostly found within pyrite and arsenopyrite. Deformation textures developed by cataclastic processes are present in arsenopyrite, pyrite, and stibnite minerals. Realgar-quartz fillings through fractures, tetrahedrite/tennantite veins cutting deformed pyrite crystals and the marcasite that replaces arsenopyrite and pyrite represent late-stage hydrothermal components. In certain samples, gold fills the discontinuities between pyrite and arsenopyrite alongside stibnite. The findings collectively impose significant early-stage constraints on the structural, mineralogical, and hydrothermal development of gold mineralization in the southern part of the Niğde Massif. All these observations indicate that gold mineralization occurred in at least two phases; may have associated with the arsenopyrite-pyrite paragenesis, and may also have been transported through discontinuities in later stages with stibnite.