PRODUCTS AND PROCESSES OF THE VUONNEMITE TRANSFORMATIONS AT THE LOW-TEMPERATURE ALTERATION OF ULTRAAGPAITIC PEGMATITES

摘要

The main occurrences of niobium minerals formed as a result of vuonnemite alteration are described. The pseudomorphs after vuonnemite from Lovozero, Khibity and Ilimaussaq alkaline massifs have been studied using optical methods, scanning electron microscopy, X-ray diffractometry, IR spectroscopy, and electron microprobe analysis. Epistolite, gerasimovskite, komarovite, Na-komarovite, and minerals of labuntsovite and pyrochlore groups have been found in the pseudomorphs composition. The main schemes of the vuonnemite alteration processes are shown as following: vuonnemite -> epistolite -> gerasimovskite; vuonnemite -> epistolite -> lueshite; vuonnemite -> epistolite -> ilimaussite; vuonnemite -> epistolite -> minerals of the labuntsovite group -> komarovite + strontiopyrochlore -> strontiopyrochlore; vuonnemite -> epistolite -> nenadkevichite -> Na-komarovite -> pyrochlore+gerasimovskite; vuonnemite -> epistolite+shkatulkalite. It is shown that Nb is more moblie than Ti under hydrothermal conditions, and fractionating of Nb and Ti is related to this stage.