| Abstract: | The composition of accessory minerals from granites of the second phase, quartz-muscovite (+fluorite), and quartz-muscovite-topaz
greisens from the Primorsky rapakivi granite complex, West Baikal region, were studied using backscattered scanning electron
microscopy. Ilmenite from granites contains inclusions of cassiterite, titanocolumbite, fergusonite-(Y), polycrase-(Y), and
betafite. Allanite-(Ce), bastnaesite-(Ce), xenotime-(Y), Y- and Zr-thorite, zircon, and cyrtolite have been identified in
granites. Greisens contain cassiterite, ferrocolumbite (Ta/Nb = 0.02−0.06), pyrochlore-group minerals, ilmenorutile, rutile,
wolframite, polycrase-(Y), monazite-(Ce), fluocerite-(Ce), bastnaesite-(Ce), cerphosphorhuttonite, thorite, and other minerals.
The ferrocolumbite + ilmenorutile assemblage is typical of quartz-muscovite greisen, whereas the rutile + ilmenorutile + wolframite
+ W-columbite assemblage is contained in the quartzmuscovite-topaz greisen as a result of an increase in Eh and decrease in
pH and potassium activity of solution in the back zone. The compositions of Th- and REE-bearing minerals indicate the important
role of phosphate and fluorine complexes in the transport of these elements. |
