Baddeleyite, zirconolite and calzirtite in lateritic rocks from Ryoke and Chichibu Terranes, Japan

Abstract

Baddeleyite, zirconolite and calzirtite were found in lateritic rocks from Ryoke and Chichibu Terranes in southwestern Japan. This is a new type of natural occurrence of the minerals. The lateritic rocks are associated with limestone widely distributed into Ryoke metamorphic and Chichibu non-metamorphic complexes. Baddeleyite, zirconolite and calzirtite are associated with Ti minerals such as anatase, ilmenite, perovskite and titanite. Calzirtite occurs simultaneously with perovskite. Rhabdophane-(Ce) like minerals also occurs in the lateritic rocks such as in emeries from Ko-Oge Island. Baddeleyite and calzirtite have compositions close to the ideal compositions, ZrO2 and Ca2Zr5Ti2O16. Zirconolite, CaZrTi2O7, accommodates significant amounts of Fe, Nb, Ta, and small amounts of Al and REE. Minor amounts of ACT are also found in the mineral. The chemical substitution in zirconolite is controlled by the reaction: REE3+ + 2(Al + Fe)3+ + (Nb + Ta)5+ ⇔ Ca2+ + 3Ti4+. Baddeleyite is a relict of the lateritization stage, or formed by the decomposition of zircon. Zirconolite formed during the prograde stage of metamorphism by the reaction; calcite + 2anatase + baddeleyite ⇔ zirconolite + CO2. The formation of calzirtite in Ca-metasomatic emery is independent from the deformation of zirconolite during the prograde stage of metamorphism.