Jaboticabal

The small intrusion of Jaboticabal is emplaced in Cretaceous basalts. To the west and northwest near Aparecida de Monte Alto, Taiuva and Piranji alkaline lavas up to 15 m thick intercalated in sandstones of the Bauru Group have been encountered in drill holes. The Jaboticabal rock is an analcime tinguaite consisting of euhedral nepheline, euhedral analcime, clear sanidine, which is less abundant than the former minerals, and aegirine-augite together with accessory magnetite, perovskite, sodic amphibole, aenigmatite, apatite, some interstitial natrolite and rare probable Zr-Ti silicates. The lavas are analcime-rich rocks (blairmorites) with no feldspar. Altered nepheline has been detected but analcime usually comprises the only salic mineral and constitutes more than half the rock. The pyroxene is titaniferous but there is some associated aegirine; perovskite, sphene and magnetite are plentiful and there is a little apatite and calcite. Chemical analyses of the tinguaite and a discussion of the relationship of this rock to the lavas will be found in Valarelli et al. (in press), and chemical analyses of the lavas in Coutinho et al. (1982).