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Oxidised gold lode stains black: the historical Encardideira (Chico Rei) deposit, Ouro Preto, Brazil

Oxidised gold lode stains black: the historical Encardideira (Chico Rei) deposit, Ouro Preto, Brazil The historical Encardideira gold mine, currently known as Chico Rei, represents a rare case of gold mine owned by a freed slave in Brazil’s colonial times. The term ‘encardideira’ alludes to the property of ingraining dirt on the surface of something. Here, we provide chemical and mineralogical evidence that the Encardideira mine likely had its name from the begriming character of its ore shoots. Gold-mineralised samples are enriched in graphite C, identified as tourmaline-enclosed euhedral graphite, and Mn-oxide minerals, mostly pyrolusite and cryptomelane-like material. Measurements for Au by atomic absorption spectrometry returned Au values above 1 ppm only after cupellation, suggesting the existence of graphite-bound gold in pervasively oxidised rocks. It is hypothesised that graphite-rich ore shoots, with superposition of Mn-oxide minerals, could account for enough gold and softness for manual removal by enslaved miners and their characteristic begriming. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Earth Science Taylor & Francis

Oxidised gold lode stains black: the historical Encardideira (Chico Rei) deposit, Ouro Preto, Brazil

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Oxidised gold lode stains black: the historical Encardideira (Chico Rei) deposit, Ouro Preto, Brazil

Abstract

The historical Encardideira gold mine, currently known as Chico Rei, represents a rare case of gold mine owned by a freed slave in Brazil’s colonial times. The term ‘encardideira’ alludes to the property of ingraining dirt on the surface of something. Here, we provide chemical and mineralogical evidence that the Encardideira mine likely had its name from the begriming character of its ore shoots. Gold-mineralised samples are enriched in graphite C, identified as...
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Publisher
Taylor & Francis
Copyright
© 2023 Institute of Materials, Minerals and Mining and The AusIMM
ISSN
2572-6838
eISSN
2572-6846
DOI
10.1080/25726838.2023.2166282
Publisher site
See Article on Publisher Site

Abstract

The historical Encardideira gold mine, currently known as Chico Rei, represents a rare case of gold mine owned by a freed slave in Brazil’s colonial times. The term ‘encardideira’ alludes to the property of ingraining dirt on the surface of something. Here, we provide chemical and mineralogical evidence that the Encardideira mine likely had its name from the begriming character of its ore shoots. Gold-mineralised samples are enriched in graphite C, identified as tourmaline-enclosed euhedral graphite, and Mn-oxide minerals, mostly pyrolusite and cryptomelane-like material. Measurements for Au by atomic absorption spectrometry returned Au values above 1 ppm only after cupellation, suggesting the existence of graphite-bound gold in pervasively oxidised rocks. It is hypothesised that graphite-rich ore shoots, with superposition of Mn-oxide minerals, could account for enough gold and softness for manual removal by enslaved miners and their characteristic begriming.

Journal

Applied Earth Science – Taylor & Francis

Published: Feb 1, 2023

Keywords: Hydrothermal graphite; Manganese-oxide minerals; Encardideira (Chico Rei) gold deposit; Ouro Preto; Minas Gerais; Brazil

References

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