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Variações composicionais de zircão em granitos anorogênicos proterozóicos do Cráton Amazônico: implicações metalogenéticas

2007; Sociedade Brasileira de Geologia; Volume: 37; Issue: 4 Linguagem: Inglês

10.5327/rbg.v37i4.1306

2317-4889

Cláudio Nery Lamarão, Roberto Dall’Agnol, Gilvana Lima da Soledade, Joseanna dos Santos Silva,

earthquake and tectonic studies

Hf-rich zircons in granitic rocks are typically associated with evolved, rare metals (Sn, Nb, Ta, W) specialized-granites. Zircons of topaz and rare-metal-bearing granites displays extremely low Zr/Hf ratios that are interpreted as a magmatic signature inherited of evolved granitic melts or as the result of hydrothermal alteration of the host rocks by F-rich fluids. This study is based essentially on images of zircon crystals, obtained through a SEM, and on semi-quantitative Energy Dispersive Spectrometry (EDS) analyses. The analyzed zircon crystals are of tin-specialized granitoids of distinct tin provinces of the Amazonian craton: the South Para, Pitinga, and Rondonia tin provinces. Zircon compositions of the A-type, not tin-mineralized granites of the Jamon Suite, southeastern of the Amazonian craton, and the Santa Rosa Granite, of the Xingu region are also presented for comparison. The zircon of the tin-specialized granites is characteristically enriched in Hf, Y, U, and Th and displays lower Zr/Hf ratios toward the more evolved facies, suggesting that magmatic differentiation was responsible for this particular feature. The zircons of the not mineralized granites show lower contents of these elements and comparatively high Zr/Hf ratios. The characteristic geochemical signature in zircons of the Tin-specialized granites indicate that zircon composition can be a useful guide to evaluate the metallogenetic potential of tin-bearing granites. A preliminary evaluation of the potential for tin in evolved granites may be based on zircon compositional studies employing EDS semi-quantitative analices obtained with a SEM. This can be an important tool for exploration surveys.