Madeira Pluton

The Madeira pluton is a granitoid intrusion situated within the Madeira suite of the Pitinga province of northern Brazil. It is ellipsoidal in character, elongated NE-SW, with an area of ~60 km2. Vertical contacts are displayed with the country rock, consisting of silicic volcanic rocks of the Iricoumé Group of the Paleoproterozoic Uatumã Supergroup. Early phases that form the outer rim include a metaluminous wiborgitic rapakivi granite intruded by a peraluminous to metaluminous biotite granite, as revealed by xenoliths of the former entrained within the latter. Intruding this is a circular stock composed of albite granite, split into a core facies of peralkaline albite granite with notable minerals including riebeckite-arfvedsonite amphibole, cryolite, pyrochlore. Surrounding this is a rim of peraluminous albite granite, fluorite-bearing, and reddish in appearance due to hematite. Gradational contacts occur between the two, with the rim facies believed to represent an autometasomatised core facies. These rocks are exploited at Pitinga mine, with major ore minerals including cassiterite (Sn), thorite (Th), and zircon (Zr). Sn contents can reach as high as ~3400 ppm within the albite granite stock. Modal compositions, petrography, and an order of emplacement can be found in Costi et al. (2009). Geochemical data can be found in Costi et al. (2009) and Lenharo et al. (2002).