Zn Mn Ilmenite in the Kuiqi Granite from Fuzhou, Fujian Province, East China

Zn-Mn ilmenite occurs as a principal constituent of the miarolitic cavities in the Kuiqi granite from Fuzhou. In the cavities potassium feldspar, albite, quartz, fluorite, aegirine and arfvedsonite also occur with accessory zircon, magnetite, hematite and sphalerite. Zn-Mn ilmenite forms a trigonal platy euhedral crystal up to 30 mm in length. Its chemical composition ranges from 37.3 to 63.8 mol.% FeTiO3 (ilmenite molecule), 61.1 to 22.4 mol.% MnTiO3 (pyrophanite molecule) and 0.6 to 15.3 mol.% ZnTiO3 (Znmetatitanate molecule). ZnO content ranges from 0.34 wt.% to 7.63 wt.%. Zonal structure is noticeable in the Zn-Mn ilmenite. FeTiO3 and ZnTiO3 molecules increase towards the crystal rim, while MnTiO3 molecule decreases towards the rim. Unit cell parameters of the rim and the core area = 5.092(6)A,c = 14.08(2)A,V = 316.1A3 anda = 5.106(7)A,c = 14.02(3)A,V = 316.6A3, respectively. Coexisting minerals, except for arfvedsonite and sphalerite, are very low in ZnO content. It is suggested that complete isomorphous replacement between FeTiO3 MnTiO3 and ZnTiO3 may be possible. Oxygen fugacity conditions for crystallization of Zn-Mn ilmenite are considered to be in the vicinity of the magnetite-hematite and quartz-fayalite-magnetite buffers.