Banca de DEFESA: Débora Ezequiel Cavalcanti

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Débora Ezequiel Cavalcanti
DATE: 04/08/2023
TIME: 14:00
LOCAL: Sala de Videoconferência do IGD
TITLE:

SPECTROSCOPY, CRYSTALLOCHEMISTRY AND FLUID INCLUSIONS OF MONTE SANTO EMERALD, TOCANTINS, CENTRAL BRAZIL.

KEY WORDS:

Monte Santo emerald; Brazilian V-dominant emerald; mineral fingerprint; mineralogy; geographic origin determination.

PAGES: 138
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

Monte Santo emeralds occur in the Araguaia Belt, Tocantins, central Brazil. The deposit was discovered in 1996 and is becoming an important source of emeralds, since they are typically of excellent quality and compare with some of the finest emeralds worldwide. Provenance is an important economic and societal issue inherent to the gems industry. Consumers increasingly aim to know the origin of their gems to ensure that their purchase does not support inhumane working conditions, cause legal problems, and to distinguish between natural, treated, and synthesized stones. This study presents, for the very first time, detailed spectroscopic, crystallochemical and fluid inclusions data for the Monte Santo emerald, in order to establish its fingerprints, making it possible to compare and distinguish it from other important emerald deposits worldwide, as well as to achieve a better understanding of the depositional-fluid characteristics, pressure-temperature emplacement conditions, and formational model. About sixty emerald samples from the Monte Santo emerald deposit were analyzed by spectroscopic methods, such as Raman spectroscopy, ultraviolet-visible-near-infrared spectroscopy (UV-Vis-NIR) and Fourier transform infrared spectroscopy (FTIR). Both major and trace element signatures were analyzed through electron microprobe analysis (EMPA). Single-crystal X-ray diffraction (XRD), was used to study its crystallographic structure. The origin of the parental fluid and the crystallization process of this deposit is very complex and the study of fluid inclusions (FIs) helped to understand its formation. Analysis of beryl chemical composition revealed the alkaline elements such as Na, K and Cs into the channels. Fluid H2O types I, II; CO2 and CH4 components were detected, as well as the presence of V, Cr and Sc as chromophore elements, their ionic charge and probable position in the crystalline structure. The Monte Santo emerald is classified into octahedral type and as alkali-rich emeralds. They are vanadium-dominant, with considerable amounts of Cr. Among significant known deposits, Monte Santo emerald has a very unique chemical composition in its combination of high V and Sc, moderate to high Cr, and low to moderate Fe concentrations. A distinctly higher Sc concentration is the main criteria that separates the Monte Santo emerald from its worldwide counterparts. The emerald deposit genesis is consistent with a multi-stage mineralizing episode derived from both metamorphic and magmatic contributions.

COMMITTEE MEMBERS:
Externo à Instituição - DANIEL ATENCIO - USP
Interno - 1336460 - FEDERICO ALBERTO CUADROS JIMENEZ
Interno - 6404885 - NILSON FRANCISQUINI BOTELHO
Externo à Instituição - RICARDO AUGUSTO SCHOLZ CIPRIANO - UFOP
Presidente - 1057547 - VALMIR DA SILVA SOUZA