U-Th-Pb Shrimp dating of hydrothermal monazite from the Trairão Gold Deposit - Alta Floresta Gold Province (Amazon Craton)

Abstract

Alta Floresta Gold Province occurs in the center-south portion of the Amazon Craton. Trairao gold deposit, which is located in the Alta Floresta Gold Province, is hosted by 1878 to 1854 Ma arc-related granites. Two important Au deposits take place in the region, the Trairao and Chumbo Grosso, which are structurally controlled by N80 degrees W/S80 degrees E trending lineament and associated with quartz veins and disseminated sulfides in a strong phyllic alteration zone of the host granite. Hydrothermal monazite grains formed during the Au mineralization event occur as fine anhedral crystals filling fractures or as isolated grains associated with Ag, Au, molybdenite, barite, pyrite, galena, and sphalerite. The hydrothermal monazite grains contain very low U, relatively low Th, and moderate Nd and La contents. SHRIMP U-Th-Pb dating of these crystals yielded an age of 1798 +/- 12 Ma for Trairao and 1805 +/- 22 Ma for Chumbo Grosso Au-deposits, whereas magmatic zircon grains of the granitic host rocks yielded an age of 1854 +/- 8 Ma. The ages obtained in this paper are similar to those reported by Assis (2015), who studied Pe Quente (Re-Os in molybdenite, 1792 +/- 9 Ma and 1784 +/- 11) and Francisco deposits (40Ar-39Ar ages from sericitic halo: 1779 +/- 6.2 and 1777 +/- 6.3 Ma). Serrato et al. (2014) acquired Re-Os dating in pyrite and molybdenite from Juruena gold deposit. The results show isochronous ages at 1786 +/- 1 Ma, with a model age at 1787 +/- 3.2 Ma, suggesting a major Statherian gold metallogenic event at the Alta Floresta Gold Province region. Regional fluids-flow has a close relationship with the generation and concentration of several important economic deposits in the Eastern border of Alta Floresta Gold Province, including Pe Quente, Francisco, Juruena, Chumbo Grosso, and Trairao Au-deposits.