Investigation of the mineralogy and geochemistry of hydrothermal alteration in Karayaşmak (Demirözü-Bayburt, NE Türkiye) and the surrounding area

This study aims to evaluate hydrothermal alteration and quantify mass changes in the Karayaşmak area (Demirözü, Bayburt, NE Türkiye) and its surroundings by utilizing alteration mineralogy and whole-rock geochemical data in order to assess the potential for valuable base metals and associated elements. The oldest unit exposed in the study area is represented by the Pulur Metamorphics. This lithostratigraphic unit, regarded as pre-Permo-Carboniferous in age and forming the basement rocks, consists of gneisses, amphibolites, schists, and metaquartzites. These rocks are unconformably overlain by the volcano-sedimentary succession of the Liassic Hamurkesen Formation, which comprises alternating sandstone, sandy limestone, mudstone, claystone, tuff, tuffite, agglomerate, and volcanic breccia. The entire sequence is covered by Quaternary alluvial deposits. Petrographic investigations indicate that the sandstones are classified as greywackes, whereas the tuffs are identified as lithic crystal tuffs. Geochemically, the tuffs display medium- to high-K calc-alkaline affinities. Their SI, CIA, and AI values support the presence of hydrothermal alteration and indicate moderate degrees of weathering. Several alteration assemblages were recognized within the tuffs, including sericitic, sericite-carbonate, chlorite-carbonate, and chloritic-propylitic alteration. Mass-balance calculations reveal that Δ(Zn+Cu +Pb) values remain relatively constant, whereas Δ(FeO+MgO) and Δ(K2O+SiO2) values generally increase. These results suggest that the alteration developed through different hydrothermal processes and that the hydrothermal fluids were relatively depleted in these base metals. Isocon analysis indicates overall mass losses ranging from 37.06% to 41.62% and mass gains between 20.14% and 48.56% in the altered tuffs. The observed mass increase is mainly attributed to the enrichment of Ca, Na, Fe, Mg, and Si. The development of hydrothermal alteration minerals within the tuffs was strongly controlled by hydrothermal fluids. The hydrothermal alteration products were most likely formed during an epithermal stage under acidic to slightly alkaline physicochemical conditions. Variations in hydrothermal alteration conditions resulted in different alteration assemblages and consequently led to distinct mass-change patterns.