Banca de DEFESA: Vivian Marjorie Braga Bandeira

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Vivian Marjorie Braga Bandeira
DATE: 02/06/2023
TIME: 08:00
LOCAL: Sala de videoconferência e Teams
TITLE:

geochemical and petrological aspects of greisen mineralizations associated with highly differentiated granites from the Zona da Bacia of the Pedra Branca Massif, Goiás

KEY WORDS:

Basin Zone; greisens; hydrothermal alteration; Tin Province of Goiás.

PAGES: 94
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

The Zona da Bacia deposit is located in the Pedra Branca Massif, northeast of the state of Goiás. The study area is inserted in the northern portion of the Tin Province of Goiás, and is characterized by hosting Sn mineralizations associated with rocks of granitic composition. These mineralizations occur in greisens and greisenized granites, formed from metasomatic events responsible for chemically and mineralogically altering the original granitic rock. This work deals with the mineralogical, geochemical and petrological characterization of the rocks of the Basin Zone, with the objective of determining the mineral phases, mineralogical assemblage and evolution of each zone of hydrothermal alteration of the deposit. Petrographic analyzes allowed classifying 4 facies of hydrothermal alteration: alteration 1, alteration 2, alteration 3 and greisens, constituted mainly by quartz, albite, potassium feldspar, and in stages with more advanced hydrothermal process, by alteration micas, topaz, cassiterite and fluorite. Mineral chemistry data in micas, obtained from electron microprobe (EPMA), show that the process of metasomatic evolution of biotite albite granite to greisen generates Fe-rich micas as a product, which transitions to a mica enriched in Al, Li and K. The geochemical mass balance performed through whole rock lithogeochemistry was able to analyze the behavior of the elements in each alteration facies, showing which elements entered and left the system during hydrothermalism. The chemical mobility studies showed that during the greisenization process, a large part of the mineralogy of the granite albite biotite was replaced by the mineralogy of the greisens. It was observed that the elements that acquired mass during the process were Al2O3, K2O, Fe2O3, MgO, MnO, Rb, Sn, Cs, Ba, Ta, Nb and Ga while the elements SiO2, Na2O, Zr, Y and W had the most expressive losses during the alteration. The results presented together with the existing literature, lead us to the conclusion that the deposit of the Basin Zone is of type A granitic association, of late/post magmatic origin, with mineralizations hosted in greisens mineralized to Sn. It is a Li-F system, and its mineralization occurs within the granitic dome itself, through the magmatic activity of the Pb2d granite, which is considered the most evolved and differentiated of the Massif, leading the fluids enriched in rare metals and Sn to the dome zone, generating mineralization with zones of intense concentration of cassiterite varying to disseminated and sterile zones. The studies confirm that the greisen-type mineralizations of the Basin Zone have genesis and chemical and mineralogical characteristics similar to those already described in the literature for other deposits, such as the greisens of the Pitinga Tin Province and the Nigerian tin deposits.

BANKING MEMBERS:
Externo à Instituição - WASHINGTON BARBOSA LEITE JÚNIOR - UNESP
Interno - 418965 - CLAUDINEI GOUVEIA DE OLIVEIRA
Presidente - 1336460 - FEDERICO ALBERTO CUADROS JIMENEZ
Interno - 1057547 - VALMIR DA SILVA SOUZA