Abstract: Field practice shows that apparent time constant (τ_s) of IP spectrum hasrelatively low dilution, and the differences in time constants between variousrocks and minerals may lead to the discovery of anomalies from orebodies ormineralizations at depth which are unlikely to be detected by parameters ofIP intensities (η_sρ_sm_s orψ_s). Using τ_s as the main parameter and also tak-ing into account all the other parameters of IP spectrum, one might distingu-ish between characteristics of IP anomalies arising from different shallow sour-ces.