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Sulfide recrystallization and gold remobilization during the 2.0 Ga stage of the Minas Orogeny: implications for gold mineralization in the Quadrilátero Ferrífero area, Brazil

Brando Soares, Mariana; Selby, David; Robb, Laurence; Corrêa Neto, Atlas Vasconcelos

Sulfide recrystallization and gold remobilization during the 2.0 Ga stage of the Minas Orogeny: implications for gold mineralization in the Quadrilátero Ferrífero area, Brazil Thumbnail


Authors

Mariana Brando Soares

Laurence Robb

Atlas Vasconcelos Corrêa Neto



Abstract

The historic Quadrilátero Ferrífero mining district in Brazil is a polydeformed Archean terrane recording several tectonic events. This history has hampered the accurate dating of its important gold deposits, given that most of the geochronological clocks have been affected by multiple thermal events. To determine an accurate time constraint for the mineralizing events in this region, we provide the first Re-Os dating for a gold deposit in the Quadrilátero Ferrífero, obtained from 13 mineral separates of disseminated sulfide phases (pyrrhotite, coarse-grained arsenopyrite, fine-grained arsenopyrite, and pyrite) at the recently discovered São Sebastião deposit (northwest Quadrilátero Ferrífero). Three distinct successive sulfidation stages are interpreted at the deposit. The final stage, texturally associated with gold, is marked by fine-grained arsenopyrite and pyrite (assemblage III) and is associated with high-temperature (~600°C) features. A Re-Os errorchron is obtained when considering the data of all samples collectively; however, a comprehensive Re-Os isochron age of 1987 ± 72 Ma (2σ; n = 4; IsoplotR model 3; initial 187Os/188Os = 2.1 ± 0.7) is obtained from assemblage III. A 187Re-187Osr isochron at 1988 ± 56 Ma (mean square of weighted deviates = 0.1, initial 187Osr = –0.1 ± 2.6 ppt; n = 4) is obtained if an initial 187Os/188Os composition of ca. 2.1, is used, this being consistent with the fact that the 187Os in the sulfides in assemblage III is largely radiogenic (187Osr). Earlier assemblages (I and II) individually show variable initial 187Os/188Os, indicative of disturbance to the Re-Os systematics at ~2.0 Ga. This age is considered the best estimate for the timing of gold mineralization at São Sebastião, being coincident with the waning stages of the Minas orogeny, the thermal effects of which are restricted to the southern Quadrilátero Ferrífero. Hence, we consider that the hot fluids from which assemblage III crystallized were responsible for resetting the Re-Os systematics in assemblages I and II and were central to Paleoproterozoic gold deposition in the region. This ~2.0 Ga age challenges previous notions of a late Archean, ~2.7 Ga mineralizing event in the Quadrilátero Ferrífero and makes it possible that gold remobilization occurred elsewhere in the region, particularly in areas representing deeper crustal levels.

Citation

Brando Soares, M., Selby, D., Robb, L., & Corrêa Neto, A. V. (2021). Sulfide recrystallization and gold remobilization during the 2.0 Ga stage of the Minas Orogeny: implications for gold mineralization in the Quadrilátero Ferrífero area, Brazil. Economic geology and the bulletin of the Society of Economic Geologists, 116(6), 1455-1466. https://doi.org/10.5382/econgeo.4830

Journal Article Type Article
Acceptance Date Dec 16, 2020
Online Publication Date Mar 19, 2021
Publication Date Sep 1, 2021
Deposit Date Apr 29, 2021
Publicly Available Date Mar 29, 2024
Journal Economic Geology and the Bulletin of the Society of Economic Geologists
Print ISSN 0361-0128
Electronic ISSN 0361-0128
Publisher Society of Economic Geologists
Peer Reviewed Peer Reviewed
Volume 116
Issue 6
Pages 1455-1466
DOI https://doi.org/10.5382/econgeo.4830

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Copyright Statement
Mariana Brando Soares, David Selby, Laurence Robb, Atlas Vasconcelos Corrêa Neto; SULFIDE RECRYSTALLIZATION AND GOLD REMOBILIZATION DURING THE 2.0 GA STAGE OF THE MINAS OROGENY: IMPLICATIONS FOR GOLD MINERALIZATION IN THE QUADRILÁTERO FERRÍFERO AREA, BRAZIL. Economic Geology 2021; doi: https://doi.org/10.5382/econgeo.4830





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