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

: 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-mag-matic, 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 discon-tinuities and craton margins. This promoted a crustal architecture composed of young, juvenile in-tra-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. orthogneiss of biotite and hornblende.


Introduction
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 major controls on the development of large orogenic gold deposits include age, temperature, and lithospheric thickness [2,3]. Enhanced asthenospheric heat input, typical of an unstable or delaminated subcontinental lithospheric mantle, promotes the devolatilization of sedimentary and/or volcanic rocks that produce metamorphic fluids in well-endowed gold provinces [4,5]. Consequently, a better understanding of the crustmantle interactions through time and lithospheric architecture has a direct impact on the economic exploration of mineral systems [6][7][8].
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). Despite its relatively small size (ca. 50,000 km 2 ), the GAB hosts several economically important gold deposits. These include the world-class Serra Grande mine, in the Crixás greenstone belt (≤7 Moz Au; AngloGold Ashanti), and deposits hosted in the Pilar de Goiás and Guarinos greenstone belts (6.5 Moz, Yamana Gold Inc.). Gold systems are hosted predominantly in Archean-Paleoproterozoic greenstone belts, and rarely in Neoproterozoic intrusions [10,11]. 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]. Previous studies in the GAB have focused on the greenstone belts, as they are the most important host for gold deposits in the region [11,[18][19][20]. Available data throughout the GAB is highly variable, with most studies focused on the north [21][22][23], and comparatively little work carried out in the south [24][25][26]. This can be partially explained by the long history of mining activity in the northern greenstone belts. Limited work in the TTG complexes, including U-Pb geochronology, Sm-Nd isotopic studies, and whole-rock geochemistry have shown that the crustal architecture of the GAB is composed of discrete lithospheric blocks of varying age, composition, and origin [21][22][23][24][25][26][27][28]. However, none of these studies have linked the isotopic characteristics of these blocks to the localization of mineral systems, as proposed for other cratonic areas such as the Yilgarn Craton, in Western Australia [29]. The ambiguous nature and still unclear origin of the GAB makes the area an exciting case study to investigate relations between crustal evolution and distribution of mineral systems.
The purpose of this work is to provide an updated appraisal of existing literature including some newly acquired data on the regional geology of the main gold deposits followed by a model for the tectono-magmatic evolution of the GAB. This dataset is used to present a more robust understanding of the crustal evolution of the craton.
Results of whole-rock analyses, in situ zircon SHRIMP U-Pb geochronology and Hf-O isotopic analyses for eight intrusive rocks in the southern GAB are reported here (Sections 2 and 3). These results challenge the paradigm of the exotic nature of the craton. Isotopic consonance across terranes suggests crustal growth by successive magmatic additions from similar sources. This is consistent with a linked, rather than exotic, evolution of terranes. The second part of the paper presents a synthesis of geological characteristics of orogenic gold mineralization in the GAB based on existing literature including new data initially presented. The third part focuses on available chemical, geochronological and isotopic data used to provide a framework of the crust-mantle evolution for the area. Long-term controversy concerning Archean crustal growth is assessed to reconcile available models. The spatial framework obtained from this geological dataset is used to infer links between crustal evolution and mineral systems, particularly gold, in the GAB.

Material and Methods
New whole-rock geochemistry, zircon U-Pb geochronology and Hf-O isotope data were obtained from eight igneous rocks in the southern GAB. Whole-rock analyses were conducted by Bureau Veritas (Perth, Australia). The samples were cast using a 66:34 flux with 4% Lithium nitrate added to form a glass bead. Major element oxides were analysed by XRF (X-ray fluorescence spectrometry). The analyses of 51 trace elements utilized fused bead laser ablation (ICP-MS). Gold, Pt and Pd were measured by Inductively Coupled Plasma (ICP) Optical Emission Spectrometry. Carbon and S were quantified by total combustion analysis, and FeO was determined volumetrically after acid digestion. The Geological Survey of Western Australia (GSWA) rock standard KG1 (Kerba Monzogranite [30]) was analysed to monitor data quality. The geochemical analyses are available in the Supplementary Table S1.
Approximately 2 kg of each sample was crushed, milled, sieved (50 mesh), panned, and magnetically separated (Frantz) to obtain heavy mineral concentrates. Non-magnetic heavy minerals were separated using LST (lithium heteropolytungstates; density of 2.95 g/mL at 25 °C). The zircon grains were handpicked, mounted in epoxy discs, and polished into two mounts (JB 1 and JB 2). Each mount included reference zircons for quality control purposes. The zircon standards used for U-Pb dating were BR266 ( 206 Pb/ 238 U and 207 Pb/ 206 Pb ages of 559.0 ± 0.5 Ma, 903 ppm U [31]) and OGC ( 207 Pb/ 206 Pb age of 3465.4 0 ± 0.6 Ma, 903 ppm U [32]). All zircon grains were imaged using the Vega 3 Tescan Scanning Electron Microprobe (SEM-EDS) at the Centre for Microscopy, Characterisation and Analysis (CMCA) at UWA. Electronic microscopy included secondary electron (SE), backscatter (BSE), and cathodoluminescence (CL) images to study the morphology of the zircon grains, e.g., growth patterns, inclusions, and fractures, for spot location. The images were obtained using an accelerating voltage of 20 kV, a working distance of 15 mm, and a beam intensity of 1.5 nA.
Analysis of selected zircons was conducted using the SHRIMP II (Sensitive Highmass Resolution Ion Microprobe) at the John de Laeter Centre (Curtin University), based on the methodology of Compston et al. [33]. Raw data was reduced with the program SQUID [34] and processed with IsoPlot v. 3.71 [35]. The U-Pb concordia diagrams, weighted average, and probability plots were plotted at a 95% confidence level (2σ).
Oxygen and hafnium isotope analyses were conducted in the same area of previous U-Pb dating. In situ Hf-O isotopic measurements were preferentially undertaken on zircon grains with less than 10% U-Pb age discordance. However, since ancient lead loss can also result in trends sub-parallel to the concordia over millions of years (e.g., [36]), concordance alone might be an unreliable disturbance index in Archean zircons [37]. Zircon oxygen isotope composition was measured by secondary ion mass spectrometry (SIMS) using a Cameca IMS 1280 multi-collector ion microprobe at the CMCA (UWA). Hafnium isotope analysis was conducted using a Thermo Scientific Neptune Plus multi-collector ICP-MS combined with a 193 nm Ar-F excimer laser sampling system in the School of Earth Sciences at UWA. The technique for oxygen analyses followed Nemchin et al. [38] and Whitehouse and Nemchin [39], whereas analytical protocols for hafnium analyses followed Kemp et al. [40]. The data reproducibility was evaluated by quality control analysis using reference zircons Penglai, OGC, FC1, and Mud Tank. The εHf values for analysed sample zircons were calculated using a 176 Lu decay constant of 1.865 × 10 −11 yr −1 [41], and the chondritic values of Bouvier et al. [42]. Averages of the U-Pb, Hf, and O isotope results for each sample are listed in Supplementary Table S2.

Petrology
The investigated rocks of the southern GAB (Supplementary Figure S1) show varying degrees of deformation, represented by homogeneous to augen-like textures (Supplementary Figures S2 and S3). A summary of their mineralogy is presented below in Table 1. The SiO2 content of the analysed samples ranges from 64.4 to 76.0 wt. % and the samples fall in the granite and quartz monzonite fields on the total alkalis-silica diagram of Middlemost [43]. K2O/Na2O ratios increase with decreasing age, except for the Serra Negra granite that shows values comparable to the ones of Archean intrusions.
In primitive mantle normalized diagrams [44,45], all samples show strong negative anomalies of high strength elements (HFSE), e.g., Ta, Nb, and Ti. Conversely, large ion lithophile elements (LILE) such as Cs, Ba, and Rb are enriched in Neoproterozoic intrusions when compared to the Archean/Paleoproterozoic intrusions. Pink Syenite and Rio Caiapó granite display a negative Eu anomaly, whereas Serra Negra and Itapuranga granites show anomalous high Ba and Sr contents.

SHRIMP Zircon U-Pb Geochronology
Geochronological results show three major peaks of igneous activity in the southern GAB during the Archean, Paleoproterozoic, and Neoproterozoic. Older magmatism is related to the formation of Archean TTGs between 2890-2820 Ma. Paleoproterozoic magmatism is represented by the 2060 Ma syn-orogenic Pink Syenite. In the Neoproterozoic two main age groups are defined by 630-610 Ma K-rich granites (i.e., Rio Caiapó, Itapuranga I and Itapuranga II) and 530 Ma Serra Negra granite. Results of SHRIMP U-Pb zircon geochronology are presented in Supplementary Tables S3 and S4. Cathodoluminescence images of representative zircon grains and concordia diagrams are provided in Supplementary Figures S4 and S5, respectively. Analyses of standard materials used for U-Pb geochronology are available in Supplementary Table S5.
Results of in situ oxygen isotope measurements of investigated rocks in the southern GAB and standard materials used to calibrate oxygen analyses are available as Supplementary Tables A8 and A9, respectively. The zircon oxygen compositions are mostly heterogeneous within samples > 2060 Ma, with standard deviations comparable to that of the reference materials (0.2 < 2σ < 0.5‰; Supplementary Table S9). A plot of δ 18 O versus emplacement age of granitic rocks in the southern GAB is provided in Supplementary Figure  S7. Oxygen isotopic compositions between 2890-2820 Ma form a scattered range from 2.1% to 7.2‰, with higher values related to younger intrusions (i.e., Paus de Choro granite). A transition to heavier oxygen isotopic compositions is recorded by 2060 Ma Pink Syenite (5.8%-7.2‰). Following considerable shift to high-δ 18 O zircons of 630-612 Ma Krich granites (8.4%-10.7‰), δ 18 O values rapidly decrease for the 530 Ma Serra Negra granite (5.6%-−6.0‰).
The polycyclic evolution of the GAB, inferred from studies concerning Archean TTG magmatism, led to its subdivision into northern and southern portions [19,21,22]. The northern portion consists of two major magmatic stages: (i) juvenile, polydeformed batholith-like tonalite, granodiorite, and granite orthogneisses with SHRIMP U-Pb zircon ages between 2840-2780 Ma and εNd +2.4 to −1.0 (Caiamar and Anta terranes), and (ii) crustalderived, dike-like granodiorite to granite gneisses with SHRIMP U-Pb zircon ages between ca. 2790-2700 Ma, and negative εNd of −2.2 (Moquém and Hidrolina terranes) [22]. The southern portion comprises the Uvá and Caiçara TTG terranes, separated by the Faina and Goiás greenstone belts ( Figure 1B). Regional studies indicate the stabilization of the GAB at ca. 2700 Ma, with crustal extension between 2500-2300 Ma [78], and closure of accretionary orogens between 2300-2050 Ma [11,15]. The TTG terranes of the GAB consist of intensely deformed orthogneisses of variable composition and age that were first delineated by gamma-spectrometry [79]. Compositionally, TTG orthogneisses vary from tonalite to granodiorite, with minor granite, charnockite, monzogranite, and adakite-like [12,23]. Available geochronology shows that TTG terranes formed during several discrete episodes dating back to 3140 Ma [23], with most preserved intrusions emplaced at 2960-2840 Ma, 2845-2785 Ma, and 2790-2700 Ma [21,22,24,25,28,77]. The 2845-2785 Ma and 2960-2840 Ma episodes are the most widespread in the northern and southern GAB, respectively, and were broadly synchronous with Archean volcanism [21,22]. The 2790-2700 Ma episode is more common in the north, and it appears to be the last magmatic event in the GAB.
There are five greenstone belts in the GAB ( Figure 3). In the north, three NNW-trending, subparallel inliers (ca. 40 km length and 6 km width) comprise, from west to east, the Crixás, Guarinos, and Pilar de Goiás greenstone belts. These greenstone belts were defined by Danni and Ribeiro [80], and Sabóia [81], with further description by Jost and Oliveira [18]. In the south, two NW-trending belts (ca. 60 km length and 5 km width) are represented, from west to east, by the Faina and Goiás greenstone belts. They both form a synclinorium offset by the NE-trending, dextral Faina fault [11,82]. The preservation of primary structures, e.g., upward younging in pelites, indicates that the southwestern limb of the Faina synclinorium is inverted whereas the northeastern limb is upright [82]. Based on the distribution of sedimentary sequences in the Faina and Goiás greenstone belts, their apparent right-lateral displacement, coupled with the contrasting sedimentation recorded in both sequences, the Faina Fault is inferred to represent a syn-sedimentary growth fault or a rift-related transform fault [82]. Stratigraphic columns for the greenstone belts in the northern and southern Goiás Archean Block (GAB). Age compilation for greenstone belts according to [11,18,71,77,82,83]. Age references for the TTGs based on [11,22,24,25,72] and this work.
All greenstone belts of the GAB were initially interpreted as synformal keels based on their geometry and lithostratigraphy [71]. However, this is currently accepted only for the two southern greenstone belts [82], whereas the northern greenstone belts are interpreted as fold-thrust belts [71]. Overall, the greenstone belts display a similar sequence of lower komatiite (400-900 m) followed by tholeiitic basalt flows (300-500 m) [71]. Primary volcanic features such as spinifex and/or cumulatic textures are locally preserved in ultramafic rocks [84][85][86]. Basaltic flows are characterized by pillow and variolitic structures with local dolerite and gabbro dikes/sills [71]. Minor BIF, gondite and/or chert lenses occur as thin layers intercalated with volcanic rocks [71,82]. The transition from lower volcanic to upper sedimentary rocks is typically marked by a tectonic unconformity. In the Faina and Goiás greenstone belts, the volcanic sequences have a maximum depositional age approximately between 2960 and 2920 Ma according to zircon U-Pb LA-ICP-MS geochronology [77], whereas in Crixás the maximum depositional age is indicated by Sm-Nd whole-rock isochron age of ca. 3000 Ma [87]. In contrast, the other two greenstone belts were formed during the Paleoproterozoic. In the Guarinos greenstone belt, lower volcanic rocks are dated at 2180 Ma [76], whereas in the Pilar de Goiás greenstone belt, volcanism is dated at 2165 Ma [11]. Unlike the lower mafic-ultramafic sequences, the overlying sedimentary units of the five greenstone belts indicate diverse depositional environments [18,82]. At Crixás, initial sedimentation is represented by carbonaceous schists typical of euxinic environments, with oolitic to stromatolitic marbles of dolomitic composition that are unconformably overlain by pelites and greywackes [88]. At Guarinos, lower chlorite-rich pelites containing clasts of basalt are laterally interlayered with basalts that are overlain by chemical sedimentary rocks (BIF, chert), conglomerate lenses and pelites [71,89,90]. At Pilar de Goiás, calcsilicate rocks, sandstone and dolomite are followed by greywackes [20].
The stratigraphy of the two southern greenstone belts was initially proposed by Danni et al. [91] as a single greenstone belt composed of lower volcano-sedimentary sequence unconformably overlain by upper sedimentary rocks. Due to their contrasting characteristics, Teixeira [92] subdivided this belt into the Faina and Goiás greenstone belts with lower komatiitic, basaltic and felsic volcanic rocks and upper siliciclastic, pelitic and chemical sedimentary rocks. The Goiás greenstone belt (previously known as Serra de Santa Rita) is characterized by lower carbonaceous-rich pelites followed by chert, BIF, and dolomite unconformably overlain by turbidites [93]. The Faina greenstone belt is characterized by two sequences consisting of lower conglomerate, quartzite and pelite overlain by chemically precipitated rocks [93].
The maximum deposition age of sedimentary rocks for all greenstone belts is constrained by a mafic dike swarm emplaced between 2500-2300 Ma [94] that crosscuts Archean TTG complexes and volcanic rocks from the Goiás, Faina and Goiás belts (but not their upper sedimentary rocks). This field relationship implies that the sedimentary rocks must have been deposited following or during regional crustal extension after 2300 Ma. The end of sedimentation is indirectly constrained by carbon isotopes of upper dolomitic rocks [75,82,95,96]. This was based on chemostratigraphic markers that reflect the oxidation of the atmosphere in the Paleoproterozoic known as the Jatuli event [97]. Upper dolomites from the northern greenstone belts and the lower sedimentary sequence from the southern greenstone belts show positive δ 13 C values (+10 to +14‰) that coupled with available geochronology indicate their deposition between 2220-2060 Ma [15,96], marking the first carbon anomaly of the Jatuli event following glaciation in the Huronian. Moreover, upper dolomites from the second sedimentary cycle of Faina and Goiás greenstone belts record mixed δ 13 C values (−0.66 to +0.66‰), which suggest their deposition at the end of Jatuli event, late in Rhyacian times and likely associated with extension in early Orosian [71].

Deformation History
The GAB shows a polyphase evolution recorded by complex deformation patterns [12]. This complexity, together with the lack of absolute dating of regional structures, has hindered a better understanding of the deformation history of the GAB, as indicated by previous studies published in the region [72,[98][99][100]. Early structural interpretations are reconsidered based on most recent geochronology and isotope geochemistry data including new data presented herein. At least three deformation events in the GAB were developed in the Archean, Paleoproterozoic, and Neoproterozoic (Table 2). These deformation events are recorded by titanite U-Pb SHRIMP dating of the Crixás Açu gneiss, which revealed distinct metamorphic episodes at 2711 Ma, 2011 Ma and 590 Ma [21,101].
The Archean Dn event was responsible for regional amphibolite facies metamorphism and deformation of all granite-gneiss TTG complexes and lower volcanic sequences of the Crixás, Faina and Goiás greenstone belts [77,87]. Structures formed during Dn include tight to isoclinal folds, thrust faults and metamorphic foliation (Sn). The amphibolite facies metamorphism is expressed by talc-serpentine-chlorite ± titanite and quartz-hornblende-biotite-epidote-titanite parallel to Sn in the volcanic rocks and TTG granitegneisses, respectively [99,102]. The contacts with adjacent granite-gneiss TTG complexes are commonly marked by deformed xenoliths of volcanic rocks in the southern belts, which suggest the greenstone belts are allochthonous [77,93]. In the northern GAB, an Archean metamorphic event, registered at ~2700 Ma, is coeval with the emplacement of younger orthogneisses [21], whereas in the southern GAB metamorphism is dated at ca. 2840 Ma [25]. The minimum age of the Dn event is provided by NE-and NW-trending mafic dikes dated by Rb-Sr (whole rock) and 40 Ar/ 39 Ar (hornblende) to 2490 ± 40 Ma, which crosscut the TTG complexes and lower volcanic rocks in the Faina, Goiás and Crixás greenstone belts [94]. In the Paleoproterozoic, D1, D2, and D3 brittle-ductile events comprise regional deformation, metamorphism and gold mineralization hosted in greenstone belts of the GAB. Early developed structures include S1 foliation developed parallel to subparallel to the bedding (S0), axial planar to tight to isoclinal folds and the inversion of the stratigraphy in the greenstone belt sequences [93,103,104]. Regional metamorphism comprises quartzchlorite-muscovite-biotite ± epidote assemblages oriented parallel to S1 foliation in the volcano-sedimentary rocks of the greenstone belts. This assemblage is compatible with greenschist to lower amphibolite facies and temperature ranges that roughly correspond to the brittle-ductile transition [105]. Gold mineralization is associated with D2 thrust faults and, to a minor extent, D3 shear zones. The Au-related hydrothermal assemblages in all deposits overprint greenschist facies metamorphic assemblages and therefore postdate peak metamorphism [12,106].
Contrasting structural evolution is recorded in the northern and southern greenstone belts for the Paleoproterozoic D1, D2 and D3 events (Table 3). In greenstone belts of the northern GAB, structures developed throughout these events include: (i) subtly ~ W-dipping S1 foliation (S0 transposed into S1), subtly W-dipping, NS-trending thrust faults, greenschist faces metamorphism and stratigraphic inversion; (ii) subtly S-dipping S2 foliation, planar axial to isoclinal F2 folds, local mm-to cm-wide shear zones, subtly N-dipping, EW-trending thrust faults and stacking of the stratigraphy; (iii) subtly E-dipping S3 foliation, subtly E-dipping, NS-trending F3 folds and lateral thrust ramps [99,103,107,108]. In the southern GAB, Paleoproterozoic deformation is largely described based on observations in the Faina greenstone belt [106]. The D1 event is expressed by moderately Ndipping S1 foliation (S0 transposed into S1), subtly W-dipping, NNW-trending F1 folds, stratigraphic inversion and greenschist facies metamorphism. The D2 event is characterized by subtly S-dipping S2 foliation, planar axial to tight to isoclinal F2 folds, gently Wplunging mineral lineation, gently S-dipping, and EW-trending thrust faults that caused stacking of the stratigraphy. The D3 event is represented by moderately N-dipping S3 foliation, NW-trending, S-dipping shear zones and subtly S-dipping thrust faults. Significant hydrothermal fluid flow along D2-related structures resulted in the development of Au-bearing quartz ± carbonate veins with only localized hydrothermal fluid flow produced during a D3 event. The timing of Paleoproterozoic deformation represented by D1 to D3 events can be stipulated by a series of intrusions emplaced between ~2170 and 2061 Ma. Early deformation is constrained by intrusion of the Posselândia diorite along the N-trending shear zone that crosscuts the Hidrolina TTG terrane and has a zircon U-Pb SHRIMP age of 2146 ± 2 Ma [109]. Mafic dikes crosscutting Au-related hydrothermal alteration in metasedimentary rocks from the Crixás greenstone belt show zircon U-Pb LA-ICP-MS age of 2170 ± 17 Ma [74]. Syntectonic granites within N-verging thrust faults in the Pilar de Goiás greenstone belt yield a zircon U-Pb SHRIMP age of 2145 ± 12 Ma [72,110]. The lower limit of the Paleoproterozoic deformation is constrained by syn-to late-tectonic Pink Syenite intrusion in the Faina greenstone belt with zircon U-Pb SHRIMP age of 2061 ± 14 Ma (Results section).
The Neoproterozoic D4 event overprints, offsets and/or reactivates previous structures. Structural features developed in D4 include subtly S-to W-plunging crenulation lineations associated with thin-skinned, E-verging thrust to reverse faults and local NStrending open folds [111]. This event is attributed to the Brasiliano/Pan-African orogeny at 650-480 Ma [112]. The timing of D4 is indirectly constrained by isotopic disturbance, e.g., Pb loss and lower concordia intercepts at approximately 600 Ma in zircon U-Pb geochronology ( [21,22,28] and this work). The maximum age range of the D4 event is constrained by a leucogranite intrusion in the Guarinos greenstone belt with U-Pb LA-ICP-MS age on hydrothermal zircon of 729 ± 15 Ma [10]. The minimum age range of this event is ascertained by the Serra Negra intrusion at the western border of the GAB with a zircon U-Pb SHRIMP age of 527 ± 5 Ma (Results section).

Gold in the Goiás Archean Block
The mineral systems of the GAB are dominated by orogenic gold deposits hosted in greenstone belts with poorly described paleoplacer and intrusion-related gold showings. Additional mineral systems recognized (but not currently economic) include minor Algoma and superior-type Fe ore, sedimentary-hosted Mn, and Au ± Cu VMS [11]. The gold deposits hosted in greenstone belts share many similarities, e.g., strong structural control, metal association, hydrothermal alteration and mineralogy, with orogenic gold deposits worldwide [113,114]. This section presents a summary of pertinent structural, mineralogical, hydrothermal alteration, ore assemblage characteristics and hydrothermal fluid conditions of significant orogenic gold deposits and occurrences in the GAB.

Deposit Structural Controls
The location of the gold deposits and the geometry of the ore shoots display strong structural control, with mineralization typically hosted in intensely deformed zones associated with shear zones [12,95]. At the regional and camp scales, high-grade gold deposits (>2 g/t Au) are spatially associated with thrust and/or strike-slip faults, ductile-brittle shear zones and folds developed during D2 (-D3) deformation events. These structures are commonly located parallel to lithological contacts such as those between the volcanosedimentary sequences and the surrounding TTG complexes [12]. In the northern portion of the GAB, ore bodies relate to, and are controlled by, D2 thrust faults that consistently verge to the east, dextral strike-slip faults (e.g., Engenho Velho and Faina, in the Guarinos and Faina greenstone belts, respectively), and sinistral strike-slip faults (e.g., Cachoeira do Ogó, in the Pilar de Goiás greenstone belt) [12]. At a deposit scale, ore shoots typically comprise elongated (up to 1500 m) bodies with down-plunge continuity parallel to a prominent stretching lineation developed in hydrothermal minerals and are particularly developed along high-strain shear zones [12,95]. Another important control on high-grade ore shoots is illustrated by the intersection of fault zones or shear zone planes with the dip of metamorphosed volcanic or sedimentary rocks. Where the fault zone or shear zone crosscuts chemically favourable units, e.g., carbonaceous schist and BIF (Mina Nova and Sertão deposits in the Crixás and Faina greenstone belts, respectively), massive replacement ore bodies along strike of these rocks display an apparent stratabound mineralization style [12].

Hydrothermal Alteration and Mineralization Styles
Hydrothermal alteration zones associated with Au mineralization in the GAB indicate enrichment in SiO2, CO2, K2O and S [12]. Major controls on hydrothermal alteration include host rock chemistry, structural setting, the fluid/rock ratio, and permeability during deformation. The gold-related hydrothermal alteration typically overprints metamorphic assemblages, but the distinction between regional metamorphic host rocks and distal alteration can be subtle. Three major mineralization styles are observed in the GAB: disseminated sulfide, vein-hosted and massive sulfide ( Figure 4 and Table 4). Most deposits are associated with a single style of mineralization, although some contain more than one style (e.g., Mina III and Sertão). Disseminated sulfide is the most common mineralization style observed in the Crixás, Guarinos, Pilar de Goiás and Faina greenstone belts. It comprises disseminated pyrrhotite-arsenopyrite-pyrite ± chalcopyrite in 0.1 to 5 m-wide proximal alteration zones surrounding quartz ± carbonate veins (e.g., Mina Nova). This mineralization style consists of 1.5 m wide, 200 m long orebodies that extend up to 1000 m down plunge. It is developed in hydrothermally altered wall rock associated with ductile shear zones, typically hosted by carbonaceous schists, metavolcanic and metasedimentary Fe-rich rocks. The hydrothermal alteration consists of white mica-quartz-ankerite/siderite ± chlorite assemblages, with minor albite ± K-feldspar and associated quartz ± ankerite/siderite veins. At Sertão, proximal white mica-K-feldspar-pyrite-chalcopyrite alteration zone shows poikiloblastic textures that suggest replacement of Fe-rich carbonates by sulphides ( Figure 5). Gold (≤50 µm) is in equilibrium with pyrrhotite (e.g., Maria Lázara) and arsenopyrite (e.g., Sertão, Jordino, and Ogó), or as inclusions and fracture-fills within these sulphides, with rare free gold (≤30 µm) in both quartz veins and proximal alteration assemblages. The approximated gold fineness associated with this style of mineralization is 920 [106,107]. At the Crixás deposits, estimated production of 3 Mt of ore is reported with an average of 6 g/t Au [12], whereas at the Sertão deposit, oxidized sulfide-rich ore resulted in 256 Koz at 24.95 g/t [115].
Vein-hosted ore consists of deformed quartz ± carbonate veins locally hosted in shear zones. It forms 0.5-2 m wide, 500 m long, 1500 m down-dip orebodies that record an estimated production of 3 Mt at 8 g/t Au for deposits in the Crixás greenstone belt [12]. Despite the lack of an available ore reserve associated with this mineralization style in the Faina greenstone belt, V2 veins in the Cascavel deposit record grades of up to 4 g/t [121]. This type of mineralization is hosted by carbonaceous schist and quartzite in the Crixás and Faina greenstone belts, respectively. At the Crixás deposits (e.g., Mina III), typical white mica-carbonate-chlorite-pyrrhotite-arsenopyrite assemblages enveloping D2-related veins contain free gold (0.1-2 mm) with a fineness of 910 [12]. At Cascavel, proximal white mica-quartz ± pyrite ± chalcopyrite alteration zones developed around V2 veins display free gold (≤250 mm) with a fineness of 992 [106].  [119]; (C) native Au bordering Asp from disseminated mineralization in the Maria Lázara deposit. Dissolution microcavities in gold grains suggest remobilization processes [14]; (D) idiomorphic Asp overprinting sulphides (Py1 and Py2) in proximal BIF at the Sertão deposit [106]; (E) textural contrast of finegrained, deformed Py1 and coarse-grained, poikiloblastic Py2 after replacement of ankerite/siderite in proximal BIF at the Sertão deposit [106]; (F) siderite overprinting Py1 and being replaced by Py2 in BIF at the Sertão deposit [106]; (G) gold (≤50 µm) in equilibrium with Asp shows microfractures and dissolution features in proximal carbonaceous schist at the Sertão deposit; (H) BSE image of elongated Au (ca. 30 µm) in equilibrium with Asp with pressure shadows filled by white mica in proximal carbonaceous schist at the Sertão deposit [106], and (I) free Au (ca. 20 µm) adjacent to subhedral Asp-Py-Cpy in BIF at the Sertão deposit [106]. Abbreviations correspond to Asp: arsenopyrite, Cpy: chalcopyrite, Py: pyrite, Po: pyrrhotite, Sid: siderite, Au: gold, Wm: white mica.

Fluid Conditions
Few available studies have focused on the conditions of ore-related fluids of orogenic gold deposits in the GAB [14,95,107,122]. Fluid inclusions in quartz from disseminated massive sulfide ore in the Mina III deposit, at the Crixás greenstone belt, show highly saline fluids in the H2O-CO2-NaCl-KCl-CH4-N2 system [95]. However, quartz from veinhosted ore also from Mina III are characterized by (i) predominant low salinity (< 10 wt. % NaCl eq.), H2O-CO2-rich fluids, and (ii) subordinate saline (>8 wt. % NaCl eq.), H2O-CO2-rich fluids enriched in CH4, N2 with rare methane-and nitrogen-rich inclusions [95]. Based on fluid inclusion homogenization temperatures, the Mina III deposits were formed between 350 to 475 °C, and at pressures of 2-3 kbars [95]. Additional garnet-biotite geothermobarometry and fluid inclusion analysis in quartz from disseminated and veinhosted mineralization styles of Orebodies IV and V in the Crixás greenstone belt indicate temperatures from 428 to 580 °C, and pressures of 5.7 to 8.3 kbars [107]. The high-pressure conditions obtained by Petersen Jr. [107] are interpreted to reflect increased crustal depth at the time of mineralization. The temperature range for the formation of these deposits is comparable with greenschist to lower amphibolite facies. Additional estimates of fluid conditions for deposits hosted in other greenstone belts in the northern GAB include studies by Pulz [14,122] at the Maria Lázara and Cachoeira do Ogó deposits, in the Guarinos and Pilar de Goiás greenstone belts, respectively. According to these studies, temperature ranges from 335 to 450 °C and pressure from 2 to 3 kbars are associated with hydrothermal fluids in these deposits. In the Faina greenstone belt, chlorite and arsenopyrite geothermometry suggest temperatures of 330-400 °C and 320-430 °C for the Cascavel and Sertão deposits, respectively [106]. Thus, the deposits of the GAB have estimated fluid temperatures and hydrothermal alteration assemblages (Table 5) comparable with other mesothermal greenstone-hosted orogenic gold deposits worldwide [1,13].
The transport and precipitation of gold in orogenic Au deposits of the GAB is interpreted to have occurred by several different mechanisms, as evidenced by contrasting occurrence and composition of gold. Major controls include destabilization of sulfide and chloride complexes, phase immiscibility and variations in pH and fO2. Mineralization during episodic flow of hydrothermal fluids (e.g., [123]) is widely attributed to gold deposits in the GAB. Evidence for the multistage precipitation of ore-related minerals is illustrated by (i) distinct paragenetic generation of ore-related mineral phases, (ii) contrasting Ag contents of gold (e.g., Maria Lázara deposit; [124]), (iii) free and refractory gold (e.g., Cascavel and Sertão deposits; [106]), (iv) crack-and-seal textures in vein-hosted mineralization (e.g., [14]), and (v) dissolution of ore-related minerals such as arsenopyrite (e.g., [122]).
In several deposits, including Cachoeira do Ogó and Cascavel in the Pilar de Goiás and Faina greenstone belt, gold occurs as free grains in quartz veins, indicating the involvement of contrasting ore-forming processes. The deposition of free gold in D2-related veins at the Cachoeira do Ogó and Cascavel deposits is possibly caused by fluid immiscibility (or boiling) and subsequent lowering of the gold solubility [128,129]. The cause of fluid immiscibility in Au-bearing veins associated with D2 thrust faults is attributed to cyclic decompression of the hydrothermal fluid caused by seismic movement along the thrust faults and veins [130][131][132]. In this scenario, gold transport involving vein-hosted mineralization styles would be facilitated via chloride complexes (e.g., [106])

Timing of Au Mineralization
The timing of the gold mineralization event in the GAB is a matter of contention [16,95,125]. Based on the estimated age of greenstone belts, gold mineralization was initially interpreted to be Archean [80]. Subsequent studies proposed that massive sulfide orebodies in the Crixás greenstone belt (CGB) formed post-peak metamorphism associated with the Brasiliano orogeny [125]. Neoproterozoic ages for gold mineralization were reinforced by K-Ar and Ar-Ar ages from amphibole at 660-730 Ma, biotite and chloritoid at 520-580 Ma, and biotite and muscovite at ~500 Ma [133], together with a whole-rock Rb-Sr isochron of Au-bearing chlorite-garnet schist at 505 ± 7 Ma [87]. However, ages obtained from these methods are easily disturbed by subsequent thermal events and thus considered unreliable to constrain ages within polymetamorphic terranes such as the GAB [21,22].
Additional geochronological data for the gold mineralization event in the GAB is offered by more recent studies [16,72,122,134]. Arsenopyrite Re-Os of massive sulfide from the Mina III deposit in the Crixás greenstone belt is dated at 2126 ± 16 Ma [16]. In the Pilar de Goiás greenstone belt, galena Pb-Pb model age of 2025 Ma [122] gives a robust, but imprecise estimate of gold mineralization. The latter is refined by zircon U-Pb SHRIMP age of 2145 ± 12 Ma for syn-tectonic albite granite intrusion in the same belt [72]. The previous data is consistent with U-Pb SHRIMP age of 2165 ± 47 Ma obtained for hydrothermal zircon hosted in mineralized metagreywacke [134]. Therefore, a Paleoproterozoic age is presumed for the gold mineralization event in the GAB.
In the Faina greenstone belt, the maximum age of gold mineralization is indirectly constrained by 2061 Ma Pink Syenite intrusion synchronous with the Au-related deformation event (Results section). The minimum age of gold mineralization is constrained by evidence from paleoplacer deposit in basal meta-conglomerate of the Faina greenstone belt [135]. The presence of deformed clasts of Au-bearing quartz-veins, disseminated sulphides in carbonaceous schist, and gold within a fine-grained matrix suggest the paleoplacer post-dates the main Au-related hydrothermal event [135]. This is consistent with other Paleoproterozoic paleoplacer deposits, such as in the Jacobina greenstone belt in the São Francisco craton [136].

Discussion
The integration of previous data with new findings presented herein is used to propose a tectono-magmatic evolution of the GAB by reconciling available datasets with isotopic evidence for crust generation. In this section, we provide: (i) interpretations of new U-Pb, Hf-O data (Section 6.1); (ii) a geological evolution for terranes in the GAB (Section 6.2); (iii) a model for crust formation (Section 6.3), and (iv) insights into the relation between crustal architecture and gold systems in the GAB (Section 6.3).

Hf-O Isotopes through Time
Hafnium and oxygen compositions of igneous zircons from terranes in the southern GAB define a remarkable progression that implies a partially linked crustal evolutionary history. The Hf-O isotope trends define four major groups at (i) 2890-2820 Ma, (ii) ~2060 Ma, (iii) 630-610 Ma, and (iv) 530 Ma. The significance of these groups and the transitions between them are explored below.
Superchondritic to near chondritic Hf isotopic evolution across 2890-2820 Ma TTG terranes reveals at least 70 m.y. of mantle-derived magmatism by extraction of melts from similar mildly depleted reservoir. The compatible Hf isotope arrays of Archean rocks favour the consanguinity of these terranes. Conversely, analogous U-Pb magmatic ages argue for a shared Mesoarchean evolution. Older crust formation events proposed by previous studies [23,25,28] based on Sm-Nd data is contentious for two main reasons. First, Sm-Nd model ages are only applicable to estimate the timing of crust differentiation represented by single crustal extraction [137], which disagrees with dominantly negative εNd values obtained for these rocks [28]. Second, alteration of accessory minerals controlling the Nd content (e.g., monazite, allanite, apatite) can cause isotopic re-equilibrium [138,139] and disturbance of the Sm-Nd systematics is expected given the poly-metamorphic history of the GAB (e.g., [140]). Accordingly, heterogeneous Hf isotope composition and discordance on concordia diagrams of the Caiçara orthogneiss may reflect zircon overgrowths formed during younger metamorphic episodes (e.g., [140,141]).
Another finding that emerges from the Hf isotope dataset is the lack of evidence for collision pinpointed by the isotopic signature of Archean TTG intrusions. The crustal thickening and progressive reworking of older components promoted during collision are manifested by unradiogenic Hf signatures [40,142,143]. Nonetheless, isotopic and geochemical signatures for the Paus de Choro granite fall along with the trend defined by magmatic zircons of the Uvá orthogneiss, which suggests the former sampled material from the source of the latter. Accordingly, the Paus de Choro granite is developed on the margin of the Uvá terrane rather than as an exotic terrane. Additionally, considering the stratigraphic integrity between the Faina and Goiás greenstone belts that separate the Uvá and Caiçara TTG terranes, the Paus de Choro granite is presumably linked to the Uvá terrane.
Oxygen isotopic compositions of 2890-2820 Ma intrusions overall agree with values obtained for Archean igneous zircons worldwide (5.0‰ < δ18O < 7.4‰; [49]), which are interpreted as typical of magmas in equilibrium with the mantle. Low δ18O values related to high U-Pb discordance and Th/U ratios largely from the Caiçara orthogneiss suggest some degree of isotopic disturbance (Supplementary Figure S8). Radiogenic lead loss due to isotopic disturbance can be promoted by hydrothermal alteration and/or metamorphism [37,144,145].
The shift to unradiogenic Hf values recorded by 2061 Ma Pink Syenite indicates the prevalence of crustal reworking from initially more radiogenic Archean values and suggests continental collision (e.g., [40,142]). Similarly, early collision and minor reworking is suggested by the unradiogenic signature of ~ 2880 Ma inherited zircons in the Pink Syenite. The low δ18O values of inherited grains (~4‰) can reflect high-temperature alteration of the source to the magmas from which these zircons crystallized. High oxygen ratios (~6-7‰) of Pink Syenite igneous grains imply a minor supracrustal contribution.
The broad range of unradiogenic Hf signatures (−3.0 to -10.5) encapsulated by 630-610 Ma K-rich magmatism supports melting of an old crust for their formation. This agrees with negative εNd (−5.1 to −5.7) and Mesoproterozoic model ages (~1440 Ma) registered for Itapuranga granites [146], and with mixed εNd (−4.2 to +2.1) and Mesoproterozoic model ages (~1100 Ma) obtained for the Rio Caiapó granite [147]. All zircons with δ18O > 8.0‰ are confined to the 630-610 Ma age group. High δ18O ratios are diagnostic for the contribution of a component (likely sedimentary) formed by low-temperature processes (e.g., [50]). Thus, anatexis of metasedimentary crust is inferred from the elevated oxygen composition of this group. Tectonic transport of sedimentary material into depth during synchronous granite generation is reported in other collisional events along convergent margins, e.g., Lachlan and Ross-Delamerian orogens [40].
Strongly unradiogenic εHf and mantle-like δ18O values of the 530 Ma Serra Negra granite suggest the predominance of crustal reworking following a linear decrease from initial mostly near-chondritic Archean signatures. Derivation from an older sialic crust is reinforced by negative εNd (−3.0 to −4.0), 1100-1900 Ma TDM model ages [147,148], and ~2680 Ma inheritance [149]. Accordingly, similar chemistry and isotopic signatures with the Uvá orthogneiss evoke shared sources and/or similar mechanisms forming the Serra Negra granite (Supplementary Figure S9). A regression line linking εHf isotope compositions of these samples highlights identical isotopic evolution from an Archean protolith (Supplementary Figure S6). The linear decrease from ~2870 Ma mostly near chondritic signatures implies successively younger magmas likely exploited the same structural conduits as older batches. This scenario challenges the heterogeneity attributed to disparate sources and growth paths across terranes of the GAB [11,12,71].

Geological Evolution of the GAB
The tectono-magmatic history of the GAB is expressed by three main events in the Archean, Paleoproterozoic, and Neoproterozoic ( Figure 6A). Amphibolite faces metamorphism in the Archean is recorded by 2772 ± 6 Ma U-Pb zircon age and 2711 ± 34 Ma titanite U-Pb age for the Crixás-Açu gneiss in the Caiamar terrane [21,22], whereas in the southern GAB metamorphism is dated at ca. 2840 Ma [25]. This suggests that the stabilization of the GAB occurred at ca. 2700 Ma.
Two main tectonic events are recorded in the GAB during the Paleoproterozoic [22]. An early crustal extension manifested by ~2300 Ma epicratonic mafic dike swarm in TTG terranes [85,94] and a compressional deformation revealed by ~2150 Ma metamorphic titanite [72]. Contrary to the age range reported for lower stratigraphic sequences of the Crixás, Faina, and Goiás greenstone belts at ca.3000-2800 Ma, volcanism at Guarinos and Pilar de Goiás greenstone belts dates approximately 2200 Ma [11,75,76]. Yet, sedimentary rocks of all greenstone belt sequences were deposited in the Paleoproterozoic [11]. Episodic magmatism during the Paleoproterozoic is represented by: (i) 2146 Ma Posselândia diorite stock hosted in NW-trending shear zone that crosscuts the Hidrolina TTG [109], (ii) 2145 Ma albite granite emplaced within N-verging thrust faults intrusive in metasedimentary rocks of the northern greenstone belts [72], (iii) Pink Syenite intrusion coeval with Au-related deformation event in the Faina greenstone belt, and (iv) 2170 Ma mafic dikes that crosscut Au-mineralized orebodies at the Crixás greenstone belt [74].
Tectonic quiescence lasted until the Neoproterozoic when the GAB was amalgamated to the Brasília fold belt. The influence of a Neoproterozoic tectonic event is reflected by thermal disturbance recorded in granite-gneisses of the GAB. Evidence include a zircon U-Pb SHRIMP 625 Ma age interpreted to result from the anatexis of the Caiçara terrane [28] and zircon U-Pb LA-ICP-MS 729 Ma age for leucogranite intrusive in the Guarinos greenstone belt [10]. However, the interpretation of these data is contested. First, thermal disturbance of isotopic systems in polydeformed terranes does not necessarily denote an intrusive event (e.g., [28]). Secondly, the shortage of analyses, method applied and lack of synchronous magmatism brings into question the reliability of the data reported for leucogranite in the Guarinos greenstone belt. Thus, more research needs to be conducted to address these interpretations.
In the northern GAB (Figure 7), TTG magmatism occurred in two main stages spanning 70 m.y. [22]. Early stage 2845-2785 Ma tonalite to granodiorite (with minor granite) orthogneisses show juvenile εNd signatures (e.g., Anta and Caiamar terranes). Inherited zircon xenocrysts in early stage intrusions suggest the contribution of an older sialic crust of up to 3300 Ma, which does not outcrop [22]. The subsequent magmatic stage forms 2711 to 2707 Ma granodiorite to granite orthogneisses with crustal εNd signature (e.g., Moquém terrane). The isotopic zonation reflected by the εNd signature of TTG terranes in the northern GAB is interpreted to denote an eastward migration of crustal growth [22]. The diachronous evolution of TTG granite-gneiss terranes in the northern GAB is augmented by whole-rock geochemistry for these rocks [19]. According to the latter, pre-to syn-collisional early stage intrusions show sub-alkaline to calc-alkaline affinities, whereas syn-collisional to post-tectonic late-stage intrusions are calc-alkaline to metaluminous. The Caiamar terrane includes the ~2840 Ma Águas Claras and Tocambira intrusions, which are intruded by the magmatic protoliths of the 2820 Ma Crixás-Açu gneiss [22]. The Hidrolina terrane is formed by 2785 Ma granodiorite that is intruded by 2146 Ma Posselândia diorite [22,109]. The Anta terrane includes 2840-2820 Ma granodiorite orthogneisses intruded by the 2790 Ma Chapada granite [22,23,151]. Fractionated REE, particularly HREE, and slightly positive εNd (0.7) recorded by the Anta orthogneisses support the contribution of an older crust in its genesis [23].
In the southern GAB (Figure 8), two major pulses of magmatism spanning 40 m.y. in the Uvá and Caiçara terranes are recorded by mostly juvenile 3040-2930 Ma and slightly crustal-derived 2890-2820 Ma orthogneisses, e.g., Paus de Choro granite [23][24][25]77,147] and this study. Zircon age inheritance at 3090-3050 Ma suggests the involvement of up to 3100 Ma crust. Older model ages of up to 3500 Ma obtained in previous studies [147] from samples with high 147 Sm/ 144 Nd ratios may reflect fractionation of the Sm-Nd system during metamorphism [28]. In the northern GAB, volcanic sequences of the Crixás greenstone belt reveal spinifex textures [92,136] typically associated with komatiite flows [150]. Ultramafic flows are overall characterized by smoothly sloping, LREE-rich patterns, whereas basalts show flat REE patterns and slight depletion in both LREE and HREE [150]. The metabasalts of the Guarinos greenstone belt have a tholeiitic affinity, slightly fractionated REE patterns and negligible negative Eu anomaly consistent with a back-arc environment [153]. Volcanic rocks in the Pilar de Goiás greenstone belt show flat to slightly fractionated REE patterns compatible with the ones from tholeiitic lavas [96].
In the southern GAB, preserved pillowed structures in lower volcanic sequences attest to the subaqueous nature of these sequences that allowed their correlation with komatiites [77]. According to the former authors, the geochemistry of lower ultramafic rocks is characterized by tholeiitic, sub-alkaline to calc-alkaline affinities and flat REE patterns. Mafic sequences of both greenstone belts are LREE-rich, HREE-poor and show subtle negative to positive Eu anomalies [77].

Archean Crust Formation: Towards a Model
The GAB records zircon U-Pb crystallization ages and zircon inheritance peaks at 3000, 2800 and 2700 Ma ( Figure 6A). Magmatic quiescence occurs between 2930-2890 Ma (in the south) and 2840-2710 Ma (in the north). Temporal and spatial relationships between TTG plutonism and greenstone belt development require a tectonic process that allows the coeval formation of both komatiite-tholeiite basalt sequences and calc-alkaline magmatism.
An argument against plume-driven models is that basalts derived from plumes are commonly associated with low water contents and, therefore, are an unlikely source for voluminous partial melt [177]. The melting of an anhydrous source contrasts with the ubiquitous hydrous mineralogy associated with that of Archean TTGs [178]. Apart from that, the refractory and cumulus nature typical of lower mafic-ultramafic sequences is likely an infertile source for evolved magmas [177]. Yet, investigations have shown that some plume-derived basalts provide an appropriate geochemical [179] and isotopic [180] source for Archean TTGs.
Recent interpretations propose a sagduction, plume-related scenario for the early evolution of terranes in the GAB [181]. Several studies advocate for similar models to explain Archean geodynamics [164,[182][183][184][185]. According to this paradigm, granitic rocks are formed via partial melting of a thick basaltic pile in an oceanic plateau [164], which implies mantle plume magmatism. However, this hypothesis is challenged by several arguments. Based on Jost et al. [181], after the formation of ≤3300 Ma sialic crust (presently not exposed in the GAB), rifts induced by a hotspot or mantle plume led to the production of ca. 3000 Ma komatiite and pillowed basalts in an oceanic island, stratovolcano, or plateau environment. According to the same authors, diapiric emplacement of felsic magmatism attributed to the Anta and Caiamar terranes took place at least 200 m.y. after crystallization of their igneous protoliths. However, crust formation in an oceanic plateau would result in upward younging and low metamorphic grade that preclude tectonic stacking via horizontal tectonics [186]. This disagrees with high-temperature, amphibolite faces metamorphism, and stacking of the stratigraphy recorded in Archean rocks of the GAB (e.g., [11,12,72]).
The Nd isotopic record for the Anta (0.0 to 0.7; [22,23]) and Caiamar terranes (−0.6 to 2.4; [22]) implies dominantly juvenile sources. Plume-related generation of TTG in an oceanic plateau could be either by: (i) density inversion [164], (ii) melting of previous crust [155], or (iii) differentiation of underplated coeval basaltic melts. The two first options imply reworking of older sources, which conflicts with the isotopic record of these terranes. In turn, the last option would reflect higher εNd values that are also inconsistent with the juvenile signature presented by previous studies [22,23]. This is supported by the in-situ U-Pb and Hf-O dataset provided for granitic rocks in the southern GAB. Near-chondritic εHf values of 2870-2840 Ma magmatic zircons of the Caiçara and Uvá orthogneisses are consistent with a major mantle-derived input. The higher εHf values for the 2820 Ma Paus de Choro granite suggest generation by melting of juvenile crust recently formed from depleted mantle (e.g., [141]), which indicates decreasing crustal reworking over time. In contrast, unradiogenic εHf values of > 2880 Ma Pink Syenite inherited zircons suggest reworking of an older crust, but the limited dataset gives no insight into the nature of that crust.
Another point of contention involving plume-related models is whether the triangular, narrow, cusp-shaped, and kilometre-deep keel shape of the Crixás greenstone belt [187] can be used to support a plume-related model invoked for the Archean generation of continental crust in the GAB, as proposed by Jost et al. [181]. Besides the extremely limited evidence provided for vertical tectonics, the parameters used to demonstrate this hypothesis are vague. For example, there is no conspicuous record of steep regional structures in the Crixás greenstone belt. This can be partially explained by the intense deformation and low preservation of any earlier formed structures in the area. Yet, low-pressure, contact-style metamorphism characterized by isograds concentrically distributed around TTG domes varying from high-temperature (i.e., amphibolite facies) adjacent to the intrusions to low-temperature (i.e., prehnite-pumpellyite facies) away from the intrusions (e.g., [188]) is also not consistent with previous structural-metamorphic investigations conducted in the Crixás greenstone belt [11,12,18,102,125].
An additional piece of evidence against a plume-related hypothesis is that, despite being proposed to explain the formation of other granite-greenstone associations, e.g., in the Kaapvaal Craton in South Africa and the Pilbara Craton in Western Australia [189], the extremely thick mafic-ultramafic sequence characteristic of these areas (the order of several kilometres) is much more pronounced than the volcanism associated with terranes in the GAB (up to 900 m in the Pilar de Goiás greenstone belt) [11,18,71]. However, the genesis of basal supracrustal sequences in the GAB is still poorly explored and a plumerelated origin is not completely disregarded. Hybrid examples of the two end-members of models proposed for Archean crust formation are reported in other cratons (e.g., [190][191][192]). Therefore, further investigation is required to define the precise genesis of Archean crust in the GAB.
Analogous chemical composition of komatiites with modern boninites (SiO2 > 53%, Mg# > 60, TiO2 < 0.5 wt. %) [199] supports a subduction-related origin of komatiites in the southern GAB [77]. The flat REE patterns and Nb-rich contents of mafic sequences, typical of back-arc and Nb-rich basalts, reinforce the involvement of subduction processes for the genesis of volcanic rocks in these sequences [77]. Therefore, volcanism in the southern GAB is interpreted to result from fore-to back-arc rifts during accretionary extension, whereas calc-alkaline intrusions are proposed to form at transient compression by shallow subduction in the southern GAB.
In the northern GAB, a whole-rock Sm-Nd isochron age of 2825 ± 98 Ma and near zero εNd (0.6) values reported for komatiite flows in the Crixás greenstone belt [150] attest to their juvenile source. Other studies propose a depleted mantle source formed in an oceanic crust based on whole-rock Sm-Nd isochron at 2998 ± 70 Ma and εNd(T) of 2.4 for lower metavolcanic rocks of the Crixás greenstone belt [87]. Nd isotopic signature and U-Pb detrital zircon geochronology suggest juvenile sources with minor contributions of reworked crust for metasedimentary rocks of the Crixás greenstone belt [87,101]. This data agrees with the above arguments for subduction rather than a plume-related origin of these rocks. In the southern GAB, the 2061 Ma Pink Syenite intrusion is compatible with the onset and prevalence of reworking. The dashed line in Figure 6C shows the Hf isotope evolution of 2870 Ma crust (Uvá TTG) towards strongly negative zircon εHf(t) values represented by the Serra Negra granite. The trend from a 2870 Ma primitive mantle has a slope that corresponds to a 176 Lu/ 177 Hf value of 0.02, which agrees with that of a mafic crust.
Compression in Phanerozoic orogens is expressed by decreasing magmatism, isotopic flare-ups, and distinct bulk rock geochemistry (e.g., [40,143]). The transition to unradiogenic Nd/Hf isotopes in accretionary margins at this time is related to increased contamination of magmas in the upper plate. In the northern GAB, the increasingly unradiogenic Nd signature from the western to the eastern TTG terranes ( Figure 6B) favours compression. Thus, calc-alkaline intrusions are proposed to form by episodic compression during shallow subduction and eastward migration of the arc in the northern GAB (e.g., [22,201]). This is compatible with geochemical results on TTG terranes from Vargas [19]. Moreover, diagnostic geochemical and geological parameters provided by Kerr [202] for volcanic sequences from distinct tectonic settings support the arc-like signature of lower mafic-ultramafic rocks in the northern GAB greenstone belts (e.g., [153]). Nevertheless, limited Nd isotopic signature available for the supracrustal rocks, especially for Guarinos and Pilar de Goiás, hampers more detailed correlations.

Linking Crustal Architecture to Gold Mineralization
Crust generation and destruction by subduction-collision in convergent margins has shaped the continental crust throughout Earth's history [203]. The evolution of continental crust promotes a diverse lithospheric architecture that effectively controls the development of preferential pathways for magmas and fluids [7]. Crustal architecture plays a major role in the location of lithospheric-crustal scale structures controlling large orogenic Au-related hydrothermal systems [8]. The potential for mineralization in cratonic blocks worldwide is illustrated by the occurrence of gold [13,[204][205][206], base metals [207][208][209][210], and iron [211][212][213][214].
As recognized by previous studies, the addition of juvenile material into the crust enhances the gold fertility in the terrane [215][216][217]. Studies in the Yilgarn craton suggest the input of juvenile crust (εNd > 0) before and after gold mineralization acted as a potential source of this metal [29]. A similar U-Pb-O-Hf isotope approach was applied in this study to provide insights into potential links between crust-mantle evolution and the development of gold systems in the GAB (Figure 9).
The geochemistry of TTGs from the GAB indicates their formation in volcanic arcs associated with subduction zones ( [19,22,77], this work). The hypothesis that a >3200 Ma older crust may have existed, based on U-Pb and Sm-Nd TDM model ages [22,25,77], is considered equivocal for two reasons. First, the reworking of these rocks indicated by geochronology and isotopic geochemistry is more likely while the magmas are still hot rather than ~300 Ma years after their emplacement. In addition, a lack of exposed crust or inherited U-Pb ages older than 3100 Ma argues against the presence of continental crust before this time. The inherent uncertainties of Nd model ages are well known [137], and the zircon Hf isotope data show little evidence for reworking of substantially older crust ( Figure 6C). A more plausible explanation for the extraction of these primitive melts involves crustal reworking occurring shortly after emplacement of the original Archean crust.
In the northern GAB, two major magmatic events are represented by ~2770 Ma rocks with juvenile-like εNd, and ~2700 Ma rocks with εNd values indicative of crustal contribution for the formation of these magmas. The new zircon in situ U-Pb-O-Hf results (Figure 6) indicate that the crustal formation in the southern GAB likely involved the negligible reworking of an older crust of approximately 2870 Ma, which overlaps with an older magmatic event proposed by Queiroz et al. [22] for the northern GAB. This is consistent with previous interpretation by Jost et al. [25]. In turn, Archean geodynamics for the southern GAB can be defined by the following sequence as: (i) 2960-2920 Ma forearc/back-arc assembly with positive εNd (+2.2 to +2.8) indicative of a juvenile arc, followed by (ii) ca. 2800 Ma continental arc with slightly negative εNd (−0.1) that indicates minor crustal contribution during genesis of tonalite magmatism [77].

Figure 9.
Map showing available εNd and zircon εHf dataset in the Goiás Archean Block. The diachronous stabilization of TTGs is evidenced by crustal growth migration towards the east in the northern GAB, suggested by increasingly crustal input eastward, whereas dominant juvenile TTG crust in the south. References for isotopic data: [22][23][24][25]28,75,147,152] and this work.
Gold deposits in the GAB are spatially located in the greenstone belts [12], especially along major structures adjacent to their boundaries with the TTGs and at intersections of multiple regional structures (e.g., [8,218]). The metasedimentary and metavolcanic host rocks of gold deposits are mostly characterized by unradiogenic εNd [87] indicative of an old, reworked source. In the southern GAB, the emplacement of syn-to late-orogenic Pink Syenite with unradiogenic εHf signature coupled with mantle-like δ 18 O values indicates a link between mantle, crust, and gold-related deformation. Similar geochemistry, geochronology, and isotopic signatures with younger intrusions, e.g., the Serra Negra granite, and the correlation of the latter with newly discovered Cu-Au deposits in the region (e.g., Fazenda Nova; [149]) have implications for regional exploration, and they support the importance of juvenile contribution for the generation of gold deposits in the GAB.

Conclusions
The GAB is the only Archean crust in central Brazil and a significant host of important gold systems. Gold mineralization in the GAB is characterized by structurally controlled orebodies, similar white mica-quartz-pyrite ± chalcopyrite hydrothermal assemblages, as well as comparable temperature and pressure conditions of ore formation. Orebodies are mainly controlled by subtly W-to NW-dipping foliation, axial planar to subhorizontal NW-striking isoclinal folds, and gently S-dipping thrust faults. Typical host rocks include carbonaceous schist, metabasalt, quartzite, and marble. Gold-related hydrothermal alteration minerals overprint greenschist to upper amphibolite faces metamorphic assemblages, therefore, are considered to represent post-peak metamorphism.
The regional isotopic signatures of igneous and sedimentary rocks offer new insights into the genesis of gold systems and the crustal evolution of the GAB. This is promoted by a combination of geological datasets at different scales, such as geochemistry and geochronology, and emphasis on gold-related ore-forming processes. The large-scale geodynamic context presented aims to boost mineral exploration strategies in the GAB.
Available geochemistry combined with isotope-time trends are used to reconcile models for the generation of Archean crust. Similar isotopic signatures highlight the secular homogeneity across the granite-greenstone terranes of the GAB that imply these terranes shared similar magma sources, tectonic processes and/or deep-seated structures during their formation.
Gold and other minor mineral deposits (e.g., Ni deposit in the Crixás greenstone belt) tend to concentrate at the borders between greenstone belts with TTG terranes, and adjacent to tectonic boundaries. The formation and distribution of mineral deposits in greenstone belts is predicted by back-arc settings, which can supply the metal budget essential for the development of gold systems and other mineralization in the GAB, such as VMS deposits.
Supplementary Materials: The following are available online at www.mdpi.com/article/10.3390/min11090944/s1. Table S1: Geochemical data of granitic rocks of the southern GAB; Table S2. Geochronology and Isotopic dataset of granitic rocks of the southern GAB; Table S3: Results of SHRIMP U-Pb zircon geochronology; Table S4: Results of SHRIMP U-Pb analyses of Archean (-Paleoproterozoic) sample; Table S5: Mean weighted analyses of standard materials used for U-Pb dating; Table S6: Results of Lu-Hf analyses of granitic samples in the southern GAB; Table S7: Results of standard materials used to calibrate in-situ Lu-Hf analyses; Table S8: Results of oxygen isotopic analyses of granitic rocks in the southern GAB; Table S9: Results of standard materials used to calibrate in-situ oxygen analyses; Figure S1: Geological map of southern GAB with the location of analysed samples; Figure S2: Hand sample and cross-polarized photomicrograph; Figure S3: Hand sample and photomicrograph; Figure S4: Cathodoluminescence (CL) images of representative zircon grains from the southern GAM; Figure S5: Concordia diagrams for studied granitic rocks of the southern GAB; Figure S6: εHf vs crystallization and inheritance ages of intrusions; Figure S7: δ18O vs emplacement age of granitic rocks in the southern GAB.