Role of Bacterial Mats in the Formation of Rocks and Ore Minerals in Travertines of Nitric Hydrothermal Springs in the Baikal Rift Zone

摘要

The last decade has been marked by the notably increasing interest of Russian and foreign researchers in the role of microorganisms in the hydrothermal processes of rock and ore formation. The most significant achievements have been gained in the study of hydro-thermal fields in modern seas, oceans, and volcanic island-arcs. However, the hydrothermal fields in young continental rift systems have been virtually ignored. Using travertine sediments from the Garga mineral spring of the Baikal rift zone as an example, we have established that thermophile cyanobacteria can form almost monomineral calcitic rocks, as well as native gold and some accessory ore minerals therein, from hot (T= 73-75℃, pH = 7.7-7.8) slightly mineralized (0.5-1.08 g/l) sodium sulfate waters. The waters are characterized by high HCO_3~- and Ca contents (Table 1) and by the prevalence of gases (N_2 85.0-99.6 vol %). The petrochemical and geochemical properties of the Garga travertine were considered in [2, 8, 9].