Banca de DEFESA: Julia Ferreira Gonçalves

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Julia Ferreira Gonçalves
DATE: 12/05/2023
TIME: 14:00
LOCAL: Sala de videoconferência e Teams
TITLE:

The Posse Au-Te deposit, Goias Magmatic Arc, Central Brazil: Hydrothermal alteration and the telluride mineralogy.

KEY WORDS:

Brasiliano Orogeny; Goiás Magmatic Arc; Orogenic Gold; Tellurides.

PAGES: 80
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

The Au-Te Posse deposit (with reserves of 23.8 Mt (dry), average grade of 1.18 g/t, and contained mineral of 0.902 Moz) is classified as an orogenic gold deposit hosted in a granodioritic gneiss, located in the northern segment of the Goiás Magmatic Arc, central Brazil. This deposit was developed during the late stages of the Brasiliano Orogeny and was affected by a regional metamorphism of amphibolite facies and retrograded to greenschist facies. The deposit is located 5 km north of the Mara Rosa city, in the state of Goiás, Brazil. The mine, when in operation, had an open pit system with a pit that extended for 1 km in length and 40 to 70 meters in width. In this study, we discuss, based on petrographic and chemical information, the process of hydrothermal alteration of the host rocks and its association with mineralization, highlighting the importance of the telluride minerals in the metallogenetic context of the deposit. Three lithotypes are distinguished in the Au-Te Posse deposit: granodioritic gneiss (Posse gneiss), mafic metavolcanic rocks (amphibolite), and kyanite-muscovite schist. Pervasive hydrothermal alteration zones associated with gold mineralization occur at the contact between the gneiss and the amphibolite, which have been classified based on the intensity of iii alterations, their different types, and mineralogical assemblages, namely: early, intermediate, advanced, and late stages, showing variable intensities of silicification, carbonation, sulfidation, and sericitization processes. In addition to the Posse Orogenic system, a second system was identified, named as pre-orogenic system (kyanitemuscovite schist) associated with a possible source of Te, as well as other elements such as Bi, Cu, and Mo. It is important to highlight that the positive correlation between Au and Ag in Posse, both in pyrite and tellurides, indicates that part of the gold is present in pyrite as Au tellurides and Au-Ag tellurides (calaverite and sylvanite), and that other tellurides in the deposit show weak association with gold. The model for gold mineralization associated with the late stages of orogenesis in the deposit is directly related to deformation through reactivation of faults and shear zones.

BANKING MEMBERS:
Presidente - 418965 - CLAUDINEI GOUVEIA DE OLIVEIRA
Externo à Instituição - CLAUDIO GERHEIM PORTO - UFRJ
Interna - 2697315 - MARIA EMILIA SCHUTESKY
Interno - 6404885 - NILSON FRANCISQUINI BOTELHO