Linking Gold Systems to the Crust-Mantle Evolution of Archean Crust in Central Brazil

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.

Cryptic trans-lithospheric fault systems at the western margin of South America: implications for the formation and localization of gold-rich deposit superclusters

“…Similarly, the origin of structural pathways may be temporally and genetically unrelated to the processes that drive their (re-) activation at the time of ore deposit formation (e.g., earthquakes along pre-existing structures to cause fault-valve style fluid ascent and associated mineralization; e.g., Sibson, 1985;1992). In fact, the geodynamic trigger is often cited as a reactivation event, and mostly documented as part of a transient tectonic switch (e.g., transpression to transtension; e.g., Goldfarb et al, 2008;Voute et al, 2019;Trunfull et al, 2020;Trevisan et al, 2021;Wiemer et al, 2021a;Bogossian et al, 2021;Loucks, 2021). Specific geodynamic triggers may drive fertility in magmas through the creation of transient compressive stress traps in the lower crust that localize sustained magma replenishment and batch fractionation (e.g., Loucks, 2021).…”