Geology and Mineralization
The Castelo de Sonhos Formation is an isolated package of sandstones and conglomerates which form a roughly circular plateau rising 300 m above the surrounding plains. The plateau lies within the Amazon Craton, bounded on the east by volcanic, plutonic and sedimentary rocks of the Iriri-Xingu domain of the Central Amazon Province with ages dating back to ~3Ga (Santos et al., 2001; Bizzi et al., 2003), and on the west by the 2,030 – 1,860 Ma Tapajós-Parima Province, consisting of granodiorites, monzogranites and syenogranites that belong to the Creporizao and Parauari Suites. Both are intruded by the slightly younger monzo- and syeno-granite stocks of the Maloquinha Suite. The predominantly granitic Tapajós-Parima Province borders the Castelo de Sonhos Formation on the north and west.
The gold mineralization is intimately associated with the conglomerates. Strong gold mineralization is often seen with hematite alteration, and sometimes with silicification as well. But not all hematite-rich layers are gold-bearing. Although gold is predominantly found in conglomerate, it also occurs within an iron-rich hangingwall quartzite at Esperança South. Furthermore, gold is sometimes also found in iron-poor sediments of all types. In both conglomerates and quartzites, gold occurs as sub-millimeter grains within the matrix.