Geology and Mineralization
The Castelo de Sonhos property encompasses a 15km by 12km plateau in the Tapajós region of Pará state. It has an average elevation of 650 meters (a.s.l.) and around 300-350 meters above the surrounding plains.
The Castelo de Sonhos Formation is a package of sandstones and conglomerates which form a roughly circular plateau. 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. The main alteration types are hematite and silicification.
Two billion years ago, a large continent lay near the South Pole, with a chain of lode gold deposits along its central mountain ridge. Gold accumulated in placer deposits down-slope, in alluvial fans, on beaches and in the near-shore marine environment. In modern times, these now include gold deposits at Tarkwa, Jacobina and Castelo de Sonhos.
There are at least two styles of paleoplacer deposits: Witwatersrand (the largest single gold producing district in the world) and Tarkwa. There are many differences such as age, type of iron in the matrix and size, but two fundamental differences are:
- Wits contains detrital carbon; Tarkwa is carbon-free
- Wits pebbles are gold-free (Frimmel, pers. comm.). Tarkwa pebbles sometimes contain gold