МИНЕРАЛЫ ГРУППЫ ШПИНЕЛИ В ПОРОДАХ ХИБИНСКОГО ЩЕЛОЧНОГО МАССИВА (КОЛЬСКИЙ ПОЛУОСТРОВ)

Abstract

Seven spinel group minerals have been revealed within rocks of Khibiny massif, in various geological positions. Hcrcynite, gahnite and vuorclainenitc occur, without exception, only in hornfellcd xenoliths of volcanogc-nic-scdimentary rocks, spinel and magnesiochromite - in alkaline-ultrabasic rocks of dyke series. Franklinite has been discovered in a low-temperature hydrothermal vein. Magnetite is widespread everywhere - in foyaites, foidalitcs, alkaline-ultrabasic rocks and up to pcgmatite-hydrothermal veins; it may even be the principal mineral in some varieties of foidalitcs. The spinel group minerals arc characterized by wide variations of their chemical compositions due to, first of all, processes of differentiation within nephcline syenites which have accompanied formation of the Main ring of foidolites and apatite-nephcline ores. There has been detected for magnetite, as for most of other through-going minerals, a directed change of its chemical composition along the radial profile, from the contact with host Protcrozoic volcanites up to geometric center of the massif: step-by-step toward the center, the summary content of Ti and Mn in this mineral increases from 5-15 up to 40 at. %.