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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.
Acknowledgements
This contribution results from an undergraduate course for students of Geology at the Department of Geology, UFMG. The aim of the course is to take students to an ore deposit for field and underground geology, involving them in all steps from sampling and sample preparation through data acquisition and interpretation to manuscript writing. All students have effectively participated and appear as coauthors. We gratefully acknowledge Antônio Lima (Toninho da Mina) for granting us access to the underground workings of Encardideira (Chico Rei). His hospitality is remarkable. Professor Neil Phillips and an anonymous reviewer contributed with thoughtful comments that considerably improved the manuscript. Their reviews are indeed appreciated, as well as the diligent editorial handling of Dr Simon Jowitt. The CDTN authors acknowledge FINEP, CNPq and FAPEMIG. We thank Dr José Adilson Dias Cavalcanti for allowing the facsimile reproduction of his geological map (Figure 2). We also thank Kavitha Sambantham and her team for their dedicated typesetting and proof correction.
Disclosure statement
No potential conflict of interest was reported by the authors.