stripes
Juquia is an asymmetric, zoned intrusion of 14 km2 intruded into Precambrian gneisses of the Acungui Group, which are fenitized in places. The major rock types are pyroxenites, containing a titanian augite, peridotites and alkali gabbros with a circular zoned carbonatite on the western side of the complex; carbonatite dykes are widespread. Nepheline syenite is found in two areas, one of which lies to the northwest of the main complex; ijolite-melteigite is confined to several small masses, mainly rimming the carbonatite. The outer part of the carbonatite is an apatite beforsite which envelops a core of banded ankerite-dolomite carbonatite. Among accessory minerals recognized in the carbonatite are apatite, magnetite, ilmenite, baryte, pyrochlore, ancylite, norsethite, pyrite and galena. Nepheline syenites comprise K-feldspar, nepheline, aegirine-augite and biotite and are considered to represent feldspathized ijolites (Born, 1971, p. 223). The ijolites consist of nepheline, aegirine-augite and occasional biotite. Apart from the carbonatite dykes, lamprophyres and tinguaites also occur within and around the complex.
BORN, H. 1971. O complexo alcalino de Juquia. Anais do XXV Congresso Brasileiro de Geologia, 1: 223-5.
BUSHEE, J.M. 1974. Potassium-argon ages of some alkaline rocks from southern Brazil.Thesis (unpublished), University of California, Berkeley. 145 pp.
FELICISSIMO, J. 1978. The Juquia alkalic district. Morro do Serrote, Sao Paulo. Proceedings of the First International Symposium on Carbonatites, Pocos de Caldas: 313
