Geochemical and reflectance spectroscopy data integration to characterize emerald deposits: the case of the Paraná deposit, Brazil

Geochemical and reflectance spectroscopy data integration to characterize emerald deposits: the case of the Paraná deposit, Brazil

The Paraná emerald deposit is one of the few occurrences of emerald, a rare beryl variety, in Borborema Province, northeastern Brazil. We characterized the Paraná deposit by combining field geology, petrography, whole-rock geochemistry, mineral chemistry, and reflectance spectroscopy. The mineraliza...

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Bibliographic Details
Published in:Anais da Academia Brasileira de Ciências Vol. 93; no. 1; p. e20200236
Main Authors: Araújo Neto, José F, Barreto, Sandra B, Carrino, Thais A, Souza, Igor M B A, Santos, Glenda L
Format: Journal Article
Language:English
Published: Brazil Academia Brasileira de Ciências 01-01-2021
Subjects:
Brazil
Geochemistry
Geology
mineral chemistry
Minerals - analysis
MULTIDISCIPLINARY SCIENCES
Paraná emerald deposit
petrography
reflectance spectroscopy
Spectrum Analysis
Brazil
Geochemistry
mineral chemistry
Paraná emerald deposit
petrography
reflectance spectroscopy
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Summary:The Paraná emerald deposit is one of the few occurrences of emerald, a rare beryl variety, in Borborema Province, northeastern Brazil. We characterized the Paraná deposit by combining field geology, petrography, whole-rock geochemistry, mineral chemistry, and reflectance spectroscopy. The mineralization is associated with phlogopite-, actinolite-phlogopite-, and phlogopite-phengite schists, mylonitic gneisses, and several acidic rocks (e.g. granitic pegmatites/aplites, quartz ± feldspar veins) along the Portalegre Shear Zone. Emerald can be found in quartz-feldspar and aplite veins and veinlets interleaved with phlogopite- or actinolite-phlogopite schists, or within the foliation of the schists. The presence of albitites and the compositional variation of the schists suggest a metasomatic origin for emerald with variations of the metasomatic process. All these different lithotypes can be readily identified through reflectance spectroscopy especially in the range of 2,150-2,450 nm, where the main mafic minerals show absorption features related to Al-OH (phengite), and Fe-OH and Mg-OH bonds (phlogopite/actinolite). Our study shows that possible mineralized phlogopite schists can be distinguished from other sterile rocks, although point spectral analysis does not separate emerald-bearing phlogopite schists from schists without emerald due to the dominance of major phlogopite absorption features rather than emerald features.
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ISSN:0001-3765
1678-2690
1678-2690
DOI:10.1590/0001-3765202120200236