Abstract
The Goiás Archean Block (GAB) in central Brazil is an important gold district that hosts several world-class orogenic gold deposits. A better comprehension of the crustal, tectono-magmatic, and metallogenic settings of the GAB is essential to accurately define its geological evolution, evaluate Archean crustal growth models, and target gold deposits. We present an overview of gold systems, regional whole-rock Sm-Nd analyses that have been used to constrain the geological evolution of the GAB, and augment this with new in situ zircon U-Pb and Hf-O isotope data. The orogenic gold deposits show variable host rocks, structural settings, hydrothermal alteration, and ore mineralogy, but they represent epigenetic deposits formed during the same regional hydrothermal event. The overprinting of metamorphic assemblages by ore mineralogy suggests the hydrothermal event is post-peak metamorphism. The metamorphic grade of the host rocks is predominantly greenschist, locally reaching amphibolite facies. Isotope-time trends support a Mesoarchean origin of the GAB, with ocean opening at 3000–2900 Ma, and reworking at 2800–2700 Ma. Crustal growth was dominated by subduction processes via in situ magmatic additions along lithospheric discontinuities and craton margins. This promoted a crustal architecture composed of young, juvenile intra-cratonic terranes and old, long-lived reworked crustal margins. This framework provided pathways for magmatism and fluids that drove the gold endowment of the GAB.
Highlights
The formation of orogenic gold deposits in the Neoarchean, Paleoproterozoic, and Phanerozoic is associated with accretionary to collisional tectonics along convergent lithospheric boundaries that precede the stabilization of the subcontinental lithospheric mantle [1,2]
The Goiás Archean Block (GAB), the only Archean terrane recognized in central Brazil (Figure 1A), was amalgamated into the Neoproterozoic Tocantins Province during the Brasiliano/Pan-African orogeny [9]
GAB and standard materials used for quality control are available in Supplementary
Summary
The formation of orogenic gold deposits in the Neoarchean, Paleoproterozoic, and Phanerozoic is associated with accretionary to collisional tectonics along convergent lithospheric boundaries that precede the stabilization of the subcontinental lithospheric mantle [1,2]. The Goiás Archean Block (GAB), the only Archean terrane recognized in central Brazil (Figure 1A), was amalgamated into the Neoproterozoic Tocantins Province during the Brasiliano/Pan-African orogeny [9]. It consists of typical granite-gneiss TTG complexes and associated greenstone belts (Figure 1B). 50,000 km2 ), the GAB hosts several economically important gold deposits. The deposits reveal a variety of mineralization styles, host rocks and structural settings [11,12], but they all show strong structural control, CO2 , K, Fe, S enrichment, similar fluid conditions and hydrothermal alteration characteristics typical of orogenic deposits [1,13]. Field relationships and geochronology suggest these deposits formed during a regional hydrothermal event related to a Paleoproterozoic orogeny at ca. 2100 Ma [14,15,16]
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