PETROLOGIC-GEOCHEMICAL FEATURES OF BRECCIAS FROM APATITE-NEPHELINE DEPOSITS, KHIBINY

Four stages of breccia formation are distinguished in apatite-nepheline deposits of the Khibiny massif (Paleozoic): tectonic without groundmass (B-I), tectonic with silicate-phosphate groundmass of pegmatoid texture (B-II), intrusion breccias with urtite (B-III) and ijolite (B-IV) groundmass. Nepheline, apatite, and pyroxene have a specific morphology, chemical composition, gas geochemical character in the groundmass of different breccias. Total gas contents vary from 0.27 to 39.07 cm3/kg in fragments and groundmass of all breccia types. CH4 prevails; H-2, He, O2, N2, and heavy hydrocarbons C2-C5 are present in the composition of gas mixture. The rocks preserves mantle helium. Three groups of rocks are distinguished in accordance with gas geochemical data: undislocated ores, tectonic (B-I and B-II) and intrusion (B-III ans B-IV) breccias. The distribution of gas phase and Na, K, Rb, Cs, Co, Fe, Mo, Sr, and REE in the groundmass and fragments of breccias in nephelines and apatites gives evidence that there is a general trend in the evolution of these components from B-I to B-IV. The following conclusions have been made: there is a genetic relation between formation of the minerals and gases; roduced fluid influences upon the composition of magmatic injections during the brecciation process; reduced fluid is a conjugate phase of alkaline melts - the source of Khibiny massif rocks.