At Kabbaldurga, infiltration of carbonic fluids along a system of ductile shears and foliation planes has led to partial transformation of Archaean grey biotite–hornblende gneiss to coarse-grained massive charnockite at about 2.5 b.y. ago. The dehydration of the gneiss assemblage was induced by a marked metasomatic change of the reacting system from granodioritic to granitic, and obviously took place under conditions of an open system at 700–750 °C and 5–7 kb. Extensive replacement of plagioclase (An16–30) by K-feldspar through Na, Ca–K exchange reactions with the ascending carbonic fluids led to strong enrichment in K, Rb, Ba, and SiO2, and to a depletion in Ca. Progressive dissolution of hornblende, biotite, magnetite, and the accessory minerals apatite and zircon resulted in a marked depletion in Fe, Mg, Ti, Zn, V, P, and Zr. Most important is the recognition of REE mobility: with advancing charnockitization, the moderately fractionated REE distribution patterns of the grey gneisses (LaN∼270; LaN/YbN = 5–20; EuN∼27; Eu/Eu* = 0.6–0.3) give way to strongly fractionated REE patterns with a positive Eu-anomaly (LaN∼200; LaN/YbN = 20–80; EuN∼22; Eu/Eu* = 0.6–1.8). The systematic depletion especially in the HREE is due to the progressive dissolution of zircon, apatite (and monazite), which strongly concentrate the REE.