Magnesian Ilmenite and Its Role in Kimberlite Petrogenesis

Titanian clinohumite and geikielite in marbles from the Bergell contact aureole

“…In the vicinity of these inclusions the Ti-Cl show only minor compositional variation and have a nearly given : Field A ilmenites from Jacupiranga carbonatite (Mitchell 1978), Field B ilmenites from kimberlites (Mitchell 1973(Mitchell , 1977Haggerty 1975), Field C ilmenites from lamprophyres, granites, basalts and carbonatites (Prins 1972;Haggerty 1976;Bergstol 1972;Czamanske and Mihalik 1972;Giere 1984) not be specified, because xTi is nearly constant around the geikielite inclusions.…”

“…7 the compositional field of the Bergell geikielites overlaps those of ilmenites from kimberlites (Mitchell 1973(Mitchell , 1977Haggerty 1975) and from the Jacupiranga carbonatites (Mitchell 1978). From the kimberlite ilmenites however, they can be distinguished on the basis of their extremely low Cr 2 0 3 -content (see Table 2).…”

“…Geikielite, the rare magnesium analog of ilmenite, occurs as an accessory mineral in rocks with high Mg/Fe ratios. It is found in serpentinized ultramafic rocks (Kashin 1937;Efremov 1954;Trommsdorff and Evans 1980;Dietrich et al 1986), in kimberlites (Mitchell 1973(Mitchell , 1977Haggerty 1975) in carbonatites (Mitchell 1978), in metasomatically altered iron ores associated with carbonatites (Zhuravleva et al 1976) and in metamorphosed impure magnesian limestones (Murdoch and Fahey 1949;Wise 1959;Cressey 1986;Ehlers and Hoinkes 1987). Geikielite has also been reported from the gem gravels of Sri Lanka (Crook and Jones 1906).…”

Chemical abrasion of zircon and ilmenite megacrysts in the Monastery kimberlite: Implications for the composition of kimberlite melts

“…In the main Cr-poor megacryst suite at Monastery, coexisting garnet, clinopyroxene and orthopyroxene crystallised early, joined by ilmenite and phlogopite, then joined by zircon, and finally by Fe-rich olivine (Gurney et al, 1979;Moore et al, 1992). The well-known Monastery ilmenite-zircon megacryst assemblage (e.g., Mitchell, 1973;Moore et al, 1992;Griffin et al, 1997;Belousova et al, 1998) comprises large crystals (N5-15 mm) that commonly form intergrowths and are characterised by an almost complete absence of crystal faces (Figs. 1A, 2).…”

“…The ilmenite is typical kimberlitic picroilmenite with MgO up to 10-15 wt.% (e.g., Mitchell, 1973;Griffin et al, 1997). Zircon megacrysts and zircon inclusions in ilmenite are compositionally similar (Supplementary Table S1).…”