Herasymets I. Mineralogy of amorphous substances in alkaline feldspar syenites, Ukrainian Shield

On the Ukrainian Shield there are three alkaline feldspar syenite Massifs with Zr-REE mineralization. These are the Azov (Priazovsky megablock), Yastrebetsky (Volynsky megablock) and Velyka Vyska (Kirovogradsky megablock) Massifs. The main ore minerals of syenites (britholite, allanite, chevkinite and zircon) are mainly metamict and semi-metamict varieties. Metamict minerals in alkaline feldspar syenites from the Velyka Vyska Massif were investigated for the first time in this work. The characteristic of metamict minerals from the Azov and Yastrebetsky Massifs was supplemented. The zircon crystals were investigated by of X-ray diffraction (XRD) in order to compare them with the zircons from the Azov and Yastrubetsky syenite Massifs, which also contains REE are known. A comparison of the CSR parameter (coherent scattering region) of the zircons showed that the degree of structural homogeneity of the crystals from the Velyka Vyska syenite Massif is similar as in the minerals from the Yastrubetsky Massif, and smaller that in those from the Azov Massif. The correlation between REE + Y and U + Th contents in zircon was found. Moreover, the correlation between impurity elements exists when their content does not exceed 4000 ppm Th+U and 40000 ppm REE +Y. The crystals from pegmatites and kimberlites show the same correlation. On almost all diffractograms a characteristic feature of the investigated zircon is the presence of the quartz reflex in the range of 2θ = 26.5-27.5. At present time in zircons from the Azov and Yastrubetsky Massifs the quartz reflexes were not detected. A comparative analysis the shape of metamict and crystalline varieties and the rims around metamict and femic minerals has been made. The shape of amorphous britholite as well as chevkinite, allanite and even zircon resembles spherical or globular. Mostly metamict minerals have a zonal structure that is consistent with the hypothesis of the liquation droplets formation. Inside the liquation droplets could happen the next stage of liquid separation. This led to the formation of one mineral rims around another mineral. Metamict minerals from alkali feldspar syenites of the Ukrainian Shield are a source of rare metals. And also they are rich reserve for discoveries new for Ukraine mineral species. Keywords: zircon, britholite, allanite, chevkinite, amorphous, metamict, inclusion, melt, liquation, alkali feldspar syenites, Ukrainian Shield.