The Santa Fé mafic-ultramafic alkaline complex, Goiás, is a subcircular body with a rough concentric zoning of rock types, containing dunites at the center and peridotites and pyroxenites at the border. Minor rock types associated with the major units are missourites, malignites and phonolites. An essexitic body occurs as a small intrusion close to the W border of the main massif. Country rocks are leucocratic quartz-feldspatic gneisses with rare amphibolite bands. Lamprophyre dikes occur to the south, cutting Precambrian gneisses and Devonian sandstones. K-Ar determinations yielded the following ages: essexite 74.4 (± 3.4) m.y., missourite 84.7 (± 1.8) m.y., malignite, ranging from 82.6 (± 4.5) to 88.4 (± 2.7) m.y., and a lamprophyre dike 86.6 (± 4.5) m.y. These ages are similar to those determined for other complexes of the Upper-Cretaceous Iporá Group of mafic-ultramafic intrusions. Sorrounding gneisses show a whole-rock. Rb/Sr age of 467 (± 10) m.y., thus corresponding to the Brasiliano Cycle.
