Hydrogeochemical monitoring carried out in 2006-2007 allows estimation of the activity coefficient of overflowing and secondary humidifying of rich iron ores in the underground workings of the Yakovlevsky Mine. Ubiquitous manifestation of H2S of various geneses was revealed during the research. Regularities in H2S and Cl– content patterns were revealed. Zones of active water overflowing from law carboniferous limestones were mapped for the –425 and –370 m horizons. A tendency of decreasing in levels of lawcarbonic aquifer is established. Zones with various water inflows to the –425 m mine horizon were revealed.