Dados da Submissão

Título

FINGERPRINTS OF THE MONTE SANTO VANADIUM-DOMINANT EMERALD AND THEIR IMPACT ON ORIGIN DETERMINATION

Texto do resumo

Beryls (Be3Al2Si6O18) are crystal-chemically complex and highly compositionally variable gem-forming minerals, found in a variety of geologic settings worldwide. Emerald (±V, ±Cr) is its green gem variety, which is considered one of the so-called "precious gems". 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 analysis in addition to major and trace element geochemistry chemical 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. 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). 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. The Monte Santo emeralds 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.

Palavras Chave

vanadium-dominant emerald; origin determination; gem provenance; forensic geology; emerald fingerprint.