ABSTRACT
Ilmenites as an accessory phase are represented in many varieties of magmatic rocks, including normal and calc-alkaline gabbroids, diorites, pyroxenites, subvolcanic and volcanic mafic rocks of normal and high alkalinity, kimberlites, carbonatites and some schists and other formations. In gabbroids and pyroxenites from some massifs there is a dense impregnation of ilmenites observed, as well as deposits of their massive ores. Due to their mechanical strength the ilmenites are able to accumulate in the products of disintegration of rocks containing them and to form placer manifestations and deposits [Rikhvanov et al., 2001]. By chemical composition the ilmenites are usually divided into three main isomorphous series: FeTiO3-MgTiO3, FeTiO3-MnTiO3 and FeTiO3-Fe2O3. The enriched with magnesium facies of ilmenites that are presented mainly in kimberlites and carbonatites belong to picroilmenites [Frantsesson, 1968; Dawson, 1983]. MgO content in them is 4-10 wt%, while in the samples from carbonatites it sometimes reaches 20% [Malakhov, 2002]. In addition to Mg in the form of impurity in ilmenites there are usually Mn, Al, V, Zr, Hf, Zn, REE and other elements. The chemical formula of ilmenites is usually written as follows: (Fe2+, Mn, Mg) (Ti, Fe3+)O3.
