The Brehov volcanogenic and stratabound base metal and gold deposit (Eastern Slovakia): Position and genetic relations in the Internal Carpathian–Alpine Cenozoic metallogenetic belt

The Brehov ore deposit, near the village of Brehov, is located in the East Slovakian Basin 15 km south-east of the Trebišov town. A progressive development of Middle Badenian to Middle Sarmatian sedimentation and volcanism in the Brehov hydrothermally mineralized area is manifested in the article. The volcanogenic, stratabound, polymetallic (Zn, Pb, Cu) and gold sulphide deposit within the Brehov–Sirník interpreted resurgent caldera occurs in the volcanosedimentary sequence. Mineralization in the deposit, consisting of the fine-grained aggregate of sulphides, is interpreted to be of shallow water origin. It is placed mostly in the rhyodacite volcaniclastics and partly in calcareous claystone, altered and brecciated. Three types of ores – the stringer (keiko), yellow and black ore – were distinguished near the Brehov village on the basis of ore composition, being formed by successive mineralization stages. The stringer ore, consisting of the sulphide minerals, dominates in the quartz-dioritic (siliceous) rocks. The yellow ore is represented primarily by pyrite, but contains also minor chalcopyrite and quartz. The black ore is an intimate mixture of sphalerite, galena, sometimes barite and minor pyrite and chalcopyrite. Tetrahedrite and marcasite occur sporadically. The ore in all cases is fine-grained. The ore bodies are almost everywhere enclosed by clay, composed of montmorillonite, sericite and chlorite. The ore bearing fluids were probably colloids of hydrothermal origin. Textures are considered to indicate that the colloids replaced the country rocks, rather than merely filled open spaces in the rhyodacite pyroclastics and epiclastics. Despite the precious metals (mostly gold) are economically important commodity in many Kuroko type deposits, in the Brehov ore deposit they occur in volumetrically minor amounts. Visible gold is present as inclusions of native gold in major sulphide minerals, whereas silver occurs in Ag-sulphides and sulphosalts, e.g. tetrahedrite and ferberite.