Abstract
The Goiás stanniferous province in Brazil is characterized by the occurrence of cassiterite mineralization associated with the hydrothermal alteration of some 20 small granitic plutons. The age of this magmatism is middle Proterozoic and that of the related mineralization is still being debated. The available geochronological results depend of the method employed: U-Pb and Rb-Sr dating yield middle Proterozoic ages, and K-Ar dating in micas results in a Cambrian Brasiliano age. This paper presents new data obtained by the K-Ar method on mica separates and by the in situ Th(U)-Pb method on single crystals of monazite from granites and metasomatites of the Serra Branca pluton, one of these 20 stanniferous granite occurrences in the province. Dates are roughly convergent around 500 Ma according to the K-Ar method, whereas they define two ranges (500 and 1600 Ma) for computed ages by the Th(U)-Pb method. These results confirm the key role of the late thermotectonic Brasiliano event (450 to 600 Ma), which is understood to coincide with the collision of two major blocks of western Gondwana.
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