Mineralogy and trace-element geochemistry of sulfide minerals in hydrothermal chimneys from the Upper-Cretaceous VMS deposits of the eastern Pontide orogenic belt (NE Turkey)

Numerous active hydrothermal chimneys have been discovered on the modern ocean floor, and the structural, textural, and mineralogical features of these chimneys have been described in detail. However, fossil chimneys have not been widely found or studied in detail. Paleo-hydrothermal chimneys were first discovered in Late Cretaceous massive sulfide deposits in the eastern Black Sea district. The well-preserved chimney fragments typically contain distinct concentric sulfide zones. The outer zones of the chimneys contain mainly pyrite and sphalerite and lesser amounts of chalcopyrite. The sulfides within the inner zone consist predominantly of chalcopyrite, with lesser amounts of pyrite and sphalerite. The axial conduits are commonly dominated by barite gangue, with variable amounts of fahlore, sphalerite, chalcopyrite, and galena. The sulfide-rich chimney zones are also characterized by significantly higher metal contents (e.g., Cu, Zn, Fe, Se, Te, Au, Ag). Laser-ablation ICP-MS studies indicate that there is a distinct systematic trace element distribution throughout the horizontal sections of the chimneys. In general, Mn, Co, Ni, Tl, U, and V are enriched in the outermost zones of the chimneys and decrease toward the interior zones. Elements indicative of higher temperature conditions, including Mo, Se, Sn, and Cu, are generally enriched in the inner zones of the chimneys. The highest contents of most of the trace elements are present within the outer walls of the chimneys, suggesting rapid precipitation in high-gradient conditions.