The research was focused on ferruginous coated grains mostly represented by microstromatolitic oncoids from the Lower Devonian (Pragian) Řeporyje Limestone employing BSE, X-Ray diffraction, and LA-ICP-MS analyses. Although no undisputed microbial remains were recorded, we regard the above-mentioned features as indicators of biogenicity of the precipitates. Positive Eu anomalies, Nd – Ce/Ce* crossplot, and Eu/Sm and Sm/Yb ratios suggest a certain influence of hydrothermal high-temperature fluids.