On the genesis of the Lestivarites of Lestivary (Khibiny)

Abstract

The collected material with sufficient clarity proves the widespread development of metasomatic processes in the contacts of large pegmatite veins. The width of the zones of change and the intensity of the process are directly dependent on the thickness of the vein, and therefore on the reserves of components moving into the side rock. At the contacts of small veins or generally on some At a distance from them we encounter lightly colored granite-like rocks, so to speak, which have not yet reached the stage of typical lestivarite. Changes in them boil down to greater or lesser albitization of the rock, a decrease or disappearance of quartz and the appearance of alkaline bisilicates. The original minerals are orthoclase, biotite and oligoclase , are present in them in greater or lesser quantities. The process of formation of lestivarites on Lestivar is thus a process of alkaline metasomatism with the introduction of alkalis (Na) and alumina and in the presence of volatiles, mainly water. Due to them and the initial composition of the rock, intense albitization occurs, the formation of alkaline amphibole further from the contact and aegirine closer to the contact; finally, apatite, eudialyte, and sphene appear near the contact. When the rock is completely replaced, macroscopically white and sugar-like rocks are formed, often found at Lestivar and other places of external contact in the fields of migmatite development, intruded by alkaline pegmatite veins. This metasomatic process is similar to the phenomena of alkaline metasomatism described by Goldschmidt, Brögger and others in the contact zones of alkaline intrusions.