J.V. Frolova, V.M. Ladygin

Lomonosov Moscow State University, Geological Faculty; Leninskie Gory, GSP-1, 119992 Moscow, Russia

The paper describes petrophysical changes of Neogene-Quaternary volcanic rocks from Mutnovsky volcanic region under the action of hydrothermal processes. It was concluded that hydrothermal alterations lead to remarkable changes of physical and mechanical properties of rocks however the tendency of properties variation is different depending from a number of factors. Propylitization causes rocks consolidation, hardening, an increase of elastic properties, a decrease of porosity and disappearing of hygroscopic moisture. The influence of low-temperature fluids on the rocks is not so unequivocally. There can be a decrease as well as an increase of petrophysical properties. The sharp difference by properties, the structure of pore-space and the character and speed of hydrothermal alterations is observed between lavas and volcaniclastic rocks. However the primary differences between these rocks can disappear due to an intensive hydrothermal activity.