Zn-rich ilmenite and pseudorutile: subsolidus products in peraluminous granites of the Melechov Massif, Moldanubian Batholith, Czech Republic
Abstract
In Hercynian peraluminous S-type granites of the Melechov Massif (Moldanubian Batholith, Czech Republic), Zn-rich ilmenite with up to 20 wt. % ZnO formed mainly as a product of subsolidus alteration of biotite into muscovite. Ilmenite usually fills the cleavage of muscovitized biotite.
It is often accompanied by a TiO2 phase, Zn-rich pseudorutile and compositions transitional between ilmenite and pseudorutile (Fe23+Ti3O9). At the ∼1 μm scale biotite alteration produced very fine intergrowths with muscovite (±chlorite).
Subsolidus alteration of primary magmatic ilmenite with less than 0.5 wt. % ZnO led to Zn-rich oxide/oxy-hydroxide phases (≤ 5.3 wt. % ZnO), characterized by increasing Fe oxidation and decreasing Fe content (down to 15 wt. % Fe2O3).