This is a province of over 30 pipes, up to 500 metres in diameter, which extends over a northwest-trending area of 20x5 km along the Arroio Moirao Graben. Most of the pipes intrude red beds of the Caneleiras Formation, are related to fractures and occur in clusters of two or more. Dykes and apophyses are also present, and there appear to be some related lavas and pyroclastics. Rock types include trachyte, phonolite and tinguaite, and some zonation in the pipes to tinguaitic margins is reflected in an increase in alkalis, etc. (Ribeiro, personal communication, 1981). Sodic pyroxene, arfvedsonite, melanite, nepheline, cancrinite, sodalite, pseudoleucite and aenigmatite occur. Spectrochemical data for a few trace elements are available (Sanchez et al. 1979).