The Miocene sediments in the Ani area contain coals and dispersed coaly particles. Reflectivity of vitrinite in core samples from boreholes was measured and the reflectivity gradients were determined. Vitrinite reflectivity increases rapidly with depth, and the reflectivity gradient reaches into 1.2% Rmxa oil/100m. This value of the gradient is anomalously high in comparison with the case of normal coalification. The reflectivity-depth curves in the boreholes indicate that the increase in vitrinite reflectivity is due to the thermal alteration caused by hidden intrusive body lying at a moderate depth. The pluton may be connected with the near-surface intrusive a bodies of dacite, which was intruded in middle Miocene times. Absence of a mosaic structure in thermally altered vitrinites indicates that the vitrinites were below bituminous rank at the time of the intrusion.