PETROLOGIC-GEOCHEMICAL FEATURES OF BRECCI AS FROM APATITE-NEPHELINE DEPOSITS, KHIBINY

Four stages of breccia formation are distinguished in apatite-nephelin e deposits of the Khibiny massif (Paleozoic): tectonic without groundm ass (B-I), tectonic with silicate-phosphate groundmass of pegmatoid te xture (B-II), intrusion breccias with urtite (B-III) and ijolite (B-IV ) groundmass. Nepheline, apatite, and pyroxene have a specific morphol ogy, 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 composi tion of gas mixture. The rocks preserves mantle helium. Three groups o f rocks are distinguished in accordance with gas geochemical data: und islocated 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 nepheline s and apatites gives evidence that there is a general trend in the evo lution 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 m agmatic injections during the brecciation process; reduced fluid is a conjugate phase of alkaline melts - the source of Khibiny massif rocks .