Gold refinement by the fractionation of Bi-enriched partial melts at the Quadrilátero Ferrífero, Brazil: implications on the formation of hypozonal deposits

Mariana Brando-Soares, Felipe Emerson André Alves, Atlas Vasconcelos Corrêa Neto, Luiz Bertolino Bertolino, Ivan Mendes Caixeta de Pamplona Araujo, Phillip Gopon, Mariana Sathler Mozart

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung


Several gold deposits display complex Bi-bearing mineralogy. Bismuth-bearing phases are generally sensitive to changes in physicochemical conditions such that the interpretation of Bi–Au associations is useful to understand these mineralizing systems. However, gaps in the physicochemical constraints given by the Bi enrichment in these systems prevent robust metallogenic models in some complex deposits. São Sebastião is a hypozonal gold deposit in the Quadrilátero Ferrífero historic mining district in Brazil, and unlike other Archean gold deposits in this area, it displays a disseminated high-temperature and high-grade sulfide overprint with Bi enrichment. The Bi-bearing mineralogy at São Sebastião is heterogeneously distributed in the BIF-hosted ore bodies. Bismuth-sulfosalts, Bi-chalcogenides, and native bismuth have crystallized in a variable set of intercalated patches, yielding different ore facies given by the fractionation of hydrothermally assisted melts. Base metal–bearing Bi-sulfosalts, electrum, and acanthite result from high-temperature (~ 600 °C) immiscible melts rich in chloride ligands, while late crystallization of high-fineness native gold associated with native bismuth at 271 °C is evidence for Au scavenging by protracted low-temperature Bi-enriched metallic melts. This mechanism has favored gold remobilization from early sulfide assemblages and the development of localized upgraded ore stringers. Rapid uplift from a reduced (low fO 2) hypozonal environment to oxidized brittle conditions is suggested by crosscutting bismuthinite-bearing veins’ fluid inclusion patterns and the absence of maldonite (Au–Bi alloy). Many hypozonal deposits like São Sebastião show similar mineralogy and have developed at the boundaries of Archean terrains, registering multiple tectonic overprints where partial melts may have had an essential role in the final ore formation.

Seiten (von - bis)781-800
FachzeitschriftMineralium deposita
Frühes Online-Datum23 Feb. 2022
PublikationsstatusVeröffentlicht - Juni 2022

Bibliographische Notiz

Funding Information:
This work was supported and financed by IAMGOLD Corporation, which authorized the publication of the data, results, and interpretations made from them.

Funding Information:
We are very grateful to Mr. Craig McDougall (IAMGOLD exploration SVP), Milton Guimarães Bueno do Prado (IAMGOLD Brazil country manager), and all the IAMGOLD staff who encouraged this study and helped in many ways to make this publication possible. This work is part of Mariana Brando Soares Ph.D. thesis, funded by grants from the Brazilian Government Research Funding Agency CNPq (142210/2016-1), and the Rio de Janeiro State Research Funding Agency FAPERJ (TEC-Nota 10; 230521). We also would like to thank IAMGOLD technicians Vander Lúcio and Janderson Muniz for preparing our samples; Leonardo Borghi, head of LAGESED, for making the microscopy facilities available; Reiner Neumann and Gustavo Pires for making the Raman spectroscopy facility available at CETEM and for helping with the FI analyses; Laboratório de Criogenia at CT (UFRJ) for making the nitrogen gas available for the FI studies; and, finally, Laurence Robb for supporting valuable discussions during the preparation of this paper. We thank editors Georges Beaudoin and David Dolejs together with two anonymous reviewers for revising and improving the final version of this paper.

Publisher Copyright:
© 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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