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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 and Selby, David and Robb, Laurence and Corrêa Neto, Atlas Vasconcelos (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., 116 (6). pp. 1455-1466.

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.

Item Type:Article
Full text:Publisher-imposed embargo until 01 September 2022.
(AM) Accepted Manuscript
File format - PDF
(7136Kb)
Status:Peer-reviewed
Publisher Web site:https://doi.org/10.5382/econgeo.4830
Publisher 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
Date accepted:16 December 2020
Date deposited:30 April 2021
Date of first online publication:19 March 2021
Date first made open access:01 September 2022

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