Banca de QUALIFICAÇÃO: Valentina Bocanegra Olivera

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : Valentina Bocanegra Olivera
DATE: 08/12/2023
TIME: 09:00
LOCAL: Sala de videoconferência e Teams
TITLE:

Deciphering the magmatichydrothermal evolution of the gold mineralization at the Rhyacian Au-Cu Lavra Velha deposit, Bahia, Brazil.

KEY WORDS:

IOCG, Tourmaline, EPMA, Fluid source, São Francisco Craton

PAGES: 59
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

The Au-Cu Lavra Velha (LV) deposit, is located in the northern portion of the São Francisco Craton in the Bahia state of Brazil. This deposit is hosted by an extensive granite body and restricted to a set of breccias and massive ores with a high content of sulfides over magnetite/hematite with a significant content of hydrothermal tourmaline. To constrain the fluid sources, infer the evolution of late magmatic to hydrothermal phases, and determine the oredeposit model of LV, this project is developed through multiple techniques such as petrographic descriptions, mineral chemistry in silicates and sulfides, and B-O isotopic analyses. Thus, the ore body has in the deepest part of the system an incipient albite alteration, followed by massive ores, sulfide breccias, and iron oxide veins related with a significative input of quartz-tourmaline for the proximal stage, and pervasive chlorite-carbonate-epidote-quartz-magnetite in the distal part. Shallower, the deposit has an advanced process conformed by white mica enriched in Cr-Ba coexisting with euhedral magnetite replaced by hematite. Tourmaline represents an important phase in both the host granite and gold mineralization. Texturally there are 5 types of tourmalines in LV tourmaline- porphyry and granite dikes (Tur 1), sulfide breccias (Tur 2), Fe-oxides veins and breccias (Tur 3), white mica alteration (Tur 4), and late quartz-tourmaline-magnetite veins (Tur 5). The tourmalines mainly belong to the alkali group with dravite compositions and some shorlitics, without any strong differentiation through the major components. The exchange vectors that dominate are MgFe-1 and (□Al)(NaR2+)-1, with contributions on alkali-deficient exchange (□Al)(NaR2+)-1, deprotonation (AlO)(R2+OH)-1, (NaAl)(CaR2+)-1 and (□Al2)(CaR2+ 2)-1 and (□Al2)(CaR2+ 2)-1, favoring reduced conditions. Sulfide minerals such as pyrite, arsenopyrite, tennantite, chalcopyrite, galena, sphalerite, and Bi-minerals along with gold and Fe-oxide represent a unique association. The chemical analysis in sulfides indicates a rich fluid in Co, Bi, As, Cu, and Au, related with inclusions of REE- and U- minerals which help us to infer a reducedIOCG as a genetic model, in addition to the important oxide content. An intricate feature is the widespread white mica rich in Cr and Ba joined to martite and gold in the shallower part of the system, indicating more acid fluids and oxidizing conditions. Different redox conditions that could indicate different sources/fluids will be better studied with trace elements and isotopic analysis into tourmalines and sulfides.

COMMITTEE MEMBERS:
Interno - 1303786 - ELTON LUIZ DANTAS
Interno - 1336460 - FEDERICO ALBERTO CUADROS JIMENEZ
Presidente - 2697315 - MARIA EMILIA SCHUTESKY
Interna - 1644358 - PAOLA FERREIRA BARBOSA
Interno - 1057547 - VALMIR DA SILVA SOUZA