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The greenstone belts of the Crixás-Goiás Domain are economically important due to significant epigenetic gold deposits and the potential for under-researched syngenetic deposits. The gold occurrences associated with the volcanogenic massive sulfide (VMS) deposits in the region are documented only in the volcanoclastic rocks of the Digo-Digo Formation, Serra de Santa Rita greenstone belt. The objective of this work is to discuss the efficiency of the induced polarization methods in the time and frequency domains for differentiating and identifying potentially mineralized zones in the exhalites associated with the VMS-type gold of the Digo-Digo Formation. Data were acquired using a multielectrode resistivity meter with the dipole–dipole array and 10 m spacing between electrodes, as well as different current injection times (250, 1000, and 2000 ms). After the electrical data processing and inversion, the sections were integrated into ternary red-green-blue and cyan-magenta-yellow models to highlight areas of high chargeability, low resistivity, and high metal factor (frequency domain) and, thus, map the higher potential zones to host polarizable metallic minerals. The geological–geophysical model elaborated from the correlation of electrical and surface geological data allowed us to identify four anomalous areas related to potential mineralized zones. The geological data confirm that two targets are associated with the geological contacts between metamafic and intermediate metavolcanic units and the exhalative horizon. One of the targets coincides with a sulfide-rich exhalative horizon (VMS), while the last target occurs in the occurrence area of metaultramafic rocks, where gold mineralization occurrences have not been previously described, being a promising target for future investigations. [ABSTRACT FROM AUTHOR]

This work is based on the unprecedented Tectonic-Geochronological Map of Bahia (TGMBA): metallogenic implications. In the TGMBA, sixteen tectonic domains were identified, and the main mineral occurrences and deposits in each were recorded. Of the Palaeo-Mesoarchean blocks, the Gavião (GB), Serrinha (SB) and Uauá (UB) blocks were highlighted. The southern GB was formed by plate tectonics, in two stages, at ca. 3403–3378 and 3259–3240 Ma. These rocks served as basement for the Umburanas Greenstone Belt, which comprises felsic metavolcanic rocks (3147 Ma) interspersed with ocean floor mafic metavolcanics and could have been the source of the recently found orogenic gold. This crust could also have formed the basal section of the Brumado metavolcanic-sedimentary sequence, which hosts one of the most important magnesite mines in the world. The northern part of the GB hosts TTGs with ages of ca. 3642–3520 Ma, the oldest known rocks in the whole São Francisco Craton. This region served as a passive margin for the Jacobina-Umburanas Sea, where quartzites and conglomerates (3305 Ma) with detrital gold were deposited and, in the deeper portions of this sea, Mesoarchean ocean floor or Island-arc basalts (3200 Ma) with pillow-lava structures were formed. On the platform of this basin, Mn deposits were formed in association with pelites and sandstones [ABSTRACT FROM AUTHOR]

One of the greatest challenges in mineral prospectivity mapping (MPM) research nowadays is to find a solid methodology that ensures the reliability of the prospectivity model during the learning and prediction procedures. Multiple uncertainties such as the location of non-deposit sites or the type of machine learning algorithm (MLA) can bias the MPM. To investigate these effects, we used multiple training datasets with different non-deposits locations, randomly created, and MLAs such as Artificial Neural Network (ANN), Random Forests (RF) and Support Vector Machine (SVM), to model orogenic-Au prospectivity in the Pitangui Greenstone Belt (PGB, Brazil). Regarding the implications in the methodology for MPM, there are great differences between the models' performances in mapping prospective zones when there is a slightly change in the location of negative samples. These changes can be observed by using the Shapley additive explanation metrics (SHAP values), which can help mitigate such effects by choosing an optimal model among all randomly created datasets. The SHAP values of non-deposit sites also showed that ANN and SVM present overfitting problems despite the use of balanced data. RF on the other hand outperformed in all ten datasets and showed great recognition and adjustment to the negative samples. The results presented in this research are also promising to the prospective studies in the PGB, as it shows a map capable to correctly predict 97 % of the known deposits and occurrences in 3 % of the total area and points the new frontiers for gold exploration in the PGB. • The Pitangui Greenstone Belt has great potential to host gold mineralization. • Location of negative samples influence the performance of prospectivity models. • Random Forest prospective models outstand in predict mineral deposits. • Structural framework and lithologies are the main proxies for gold exploration. [ABSTRACT FROM AUTHOR]

We use offshore 2-3D seismic reflection and potential field data coupled with field work to investigate the control of lithospheric heterogeneity and shear zone rejuvenation on the mode of extension and the architectural segmentation of the southern Angola margins. The pre-rift basement is inherited from several Precambrian deformation events ended by the Pan-African/Brasiliano orogen that accreted four different age-dependent lithospheric domains with contrasted thickness, fabrics, thermal structure, and chemical composition. From north to south, the continental crust is composed of Neoproterozoic metapelites, Paleoproterozoic gneisses and migmatites and Archean greenstone belts pervasively intruded by TTG granitoids. The latter are compartmentalized by lithospheric-scale Archean – Paleoproterozoic shear zones with a general sub-vertical fabric. Upon extension, these pre-existing shear zones nucleated extensional deformation, focalized magmatism and accommodated different rates of extension and width of offshore rift domains. In the north, younger Neoproterozoic lithospheric domain deformed with a ductile behavior and multiple crustal detachments promoting lithospheric decoupling and a distributed extension, with late continental break-up. It favored the formation of a wide magma-poor margin where extension was accommodated by low-angle, seaward-dipping extensional faults and mantle-exhumation. To the south, Archean and Paleoproterozoic lithospheric domain with stronger and brittle strength profile promoted a more localized extensional deformation and favored an early lithospheric coupling and continental break-up. This ultimately led to the formation of a short margin with increased magmatic budget, where extension was accommodated by high-angle, landward-dipping extensional faults and mantle-exhumation. We demonstrate that the pre-rift heterogeneity of the lithosphere controlled the mode of extension during the rift and the along-strike variation of margin geometry. Moreover, the rejuvenation of Precambrian shear zones as extensional transverse fault zones also promoted the activation of lithospheric-scale thermal drains facilitating the emplacement of mantle-related melts into the upper crust. • The Precambrian lithosphere of South Angola is heterogeneous in terms of structural fabrics and rheology. • Limits between basement domains consist of large sub-vertical structures referred to lithospheric-scale shear zones. • Onshore inherited shear zones extend in the rifted margin domain and are rejuvenated, both by tectonics and magmatism. • Patterns of shear zone rejuvenation are change in fault trends, margin orientation, polarity, width and magmatic budget. • Brazil – Angola pre-rift basement reconstruction responsible for rift segmentation and magmatic budged upon extension. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fractal and multifractal analyses were used to study four orogenic gold provinces. • Case study conducted on a key deposit at the local and micro scales. • Fractal dimension maps showed good correlation with known mineral occurrences. • Orogenic gold deposits showed multifractal behavior. • Multifractal indices help obtain information on gold deposits in multiple scales. Understanding the controls on the spatial distribution of mineral deposits is crucial for prospecting new occurrences. Various geological processes operate together at microscopic to macroscopic scales, generating mineral systems responsible for significant accumulations of economic minerals. This characteristic of functioning at various scales, accompanied by repetition of features over space during mineralization, indicates that these processes are self-similar, meaning they exhibit fractal geometry. Previous research has demonstrated that the combined action of processes involved in mineralization in such critical, nonlinear systems, produces objects with multifractal characteristics. Therefore, the spatial distribution of mineral deposits should be studied using appropriate methods for better understanding of their controls. In this context, this study investigated the multiscale geometric characteristics of worldclass orogenic gold systems in Archean greenstone belts using fractal and multifractal analyses. First, at the macroscopic-scale, regional-scale features were considered in the major greenstone belt provinces with orogenic gold deposits worldwide, namely: Abitibi (Canada), Norseman–Wiluna (Australia), Rio das Velhas (Brazil), and Central Lapland (Finland). Next, at an intermediate scale, local-scale features were examined in detail within the context of the Córrego do Sítio Lineament. Finally, at the microscopic scale, the focus was on the Córrego do Sítio orogenic gold deposit—a key deposit in the Rio das Velhas greenstone belt. Fractal dimensions of the spatial distributions of mineral deposits, magnetic lineaments, and their intersections were investigated at the macroscopic to local scales, as well as the spatial distribution of ore minerals at the microscopic scale, using the box-counting method. Maps of fractal dimensions of magnetic lineaments were generated and compared with the spatial distribution and tonnage of orogenic gold deposits at the regional scale. The same features were analyzed using the method of multifractal moments. The results at the three scales were analyzed and synthesized to identify meaningful patterns for understanding these orogenic gold systems. With regard to fractality, the orogenic gold deposits in all the investigated provinces exhibited unique spatial distributions at different scales, namely: less than 2–4 km, from 2 to 4 km to 10–30 km, and more than 10–30 km. The analysis of magnetic lineaments yielded a correlation between gradients of fractal dimensions and gold tonnages in the orogenic gold deposits. The multifractal analyses indicate multifractal geometries extending from the microscopic to the macroscopic scale. The calculated multifractal indices of Δα (singularity variation), τ"(1) (multifractality index), and Δf(α) (multifractal spectrum variation) showed direct relationships with endowment of orogenic gold in the studied provinces, as well as with differences in mineralization styles in thin sections. The findings demonstrate the effectiveness of the analyses used for improved characterization of the studied mineral systems; they also allow comparing similar systems at different scales and locations and they can be used to study other mineral systems with similar geological controls. [ABSTRACT FROM AUTHOR]

The Itareru tonalite is one of the Paleoproterozoic plutonic rock units that intruded the Serrinha block, an Archean-Paleoproterozoic crustal fragment of the São Francisco Craton (Bahia, Brazil). It is characterized by a ca. 80 km long, NW-SE elongated leaf-shaped body, mainly comprised of tonalite-diorite to granodiorite rocks with numerous dioritic enclaves. Magnetic studies were performed on 26 sites of the Itareru pluton (including country rocks). Anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) are coaxial, indicating that all minerals have the same orientation, partially controlled by regional strain. Rock-magnetism measurements reveal that paramagnetic–matrix minerals contributed significantly to the magnetic susceptibility and AMS while magnetite grains in the range of 2–5 μm are responsible for AARM. Magnetic fabrics in the central region of the pluton are probably primary (magmatic), which was acquired when the rocks were crystallized, reflecting magma flow linked to a magma feeder zone (magma chamber). The moderated magnetic lineation plunges in the northern part of the pluton suggest that this region was close to the feeder zone. In contrast, the southern region should be far from it, since the magnetic lineations are horizontal to sub-horizontal. The Itareru tonalite emplacement was also controlled by regional strains related to the collision of the Paleoproterozoic Rio Itapicuru greenstone Belt with the Archean basement. • AMS and AARM are coaxial indicating that all minerals have the same orientation. • Magnetic fabrics in the central region of the pluton are probably magmatic acquired when the rocks were crystallized. • Magnetic fabrics in the central region of the pluton are related to magma flow. • The emplacement of the pluton was controlled by regional strains. • Itareru emplacement is related to the collision of the RIGB with the Archean basement. [ABSTRACT FROM AUTHOR]

The world-class Cuiabá gold deposit of the Archaean Rio das Velhas greenstone belt in Brazil is hosted in banded iron formation containing carbonaceous matter and carbonate, within the reclined, isoclinal Cuiabá fold. Mineralised quartz veins are hosted in andesite in the stratigraphic footwall of the banded iron ores and form some of the more recently discovered ore bodies. Fluid inclusion data of the quartz vein–associated "Veio de Quartzo" ore body are obtained from four quartz types (Qz1, Qz2, Qz3, Qz5) in gold-mineralised V1 shear vein and V2 extensional veins, barren V3 extensional vein array, and V4 breccia-style veins, all developed during the Archaean D1 event. Three fluid types are distinguished: (i) aqueous fluids of low salinity (1.8–3.8 wt% NaCl equiv), homogenisation (into liquid) at 220 to 230 °C; (ii) aqueous fluids of moderate salinity (5.3–12.7 wt% NaCl equiv), and homogenisation at 250 to 290 °C; and (iii) aqueous-carbonic fluids of moderate salinity (6.0–15.1 wt% NaCl equiv), with 30–91 mol% CO2, 8–41 mol% CH4 and up to 28 mol% N2 and decrepitation (into vapour) at 280 to 310 °C. Based on an independent pressure estimate, a pressure correction was applied to aqueous fluid inclusions, resulting in minimum trapping temperatures at 360 °C for V1 veins, 330 °C for V2 veins, 300 °C for V3 veins and 270 °C for the late-stage V4 veins. Ion chromatography analyses reveal a Br/Cl ratio of 0.7 × 10−3 in Qz1-V1, from 1.4 to 1.5 × 10−3 in Qz2-V2, 0.3 to 0.4 × 10−3 in Qz3-V3 and 0.7 to 0.9 × 10−3in Qz5-V4 veins. Zinc, Pb and Cu are relatively enriched with ~ 100 to 1000 ppm in aqueous and aqueous-carbonic fluid inclusion assemblages in all vein and quartz types, which is similar to other orogenic gold deposits hosted in the Rio das Velhas greenstone belt. The fluid inclusion data are consistent with a model invoking a metamorphic origin for the mineralising fluid. A two-step model of hydrothermal fluid flow and gold enrichment is suggested to have developed during the Archaean D1 event, with an early, aqueous-carbonic fluid pulse of relatively high temperature (from V1 up to V3) and an evolved, aqueous-carbonic fluid pulse of lower temperature (V4, breccia-style veins). The Rio das Velhas greenstone belt is dominated by regionally metamorphosed metasedimentary rocks, resulting in a complex hydrothermal fluid evolution and related gold mineralisation such as the shear zone–controlled Veio de Quartzo ore body. [ABSTRACT FROM AUTHOR]

Hypozonal orogenic gold mineralization has been recently recognized in the Troia Massif, an Archean/Paleoproterozoic basement inlier within the Neoproterozoic Borborema Province, NE Brazil. The mineralization occurs in association with quartz veins hosted by the amphibolite facies Paleoproterozoic Serra das Pipocas greenstone belt. The main mineralized areas are located near parallel to lithological contacts, siting on shear zones established at the metavolcanic and metasedimentary boundary. Four deformation events are recognized: (1) Dn was responsible for the early Sn foliation, parallel to the bedding (So) of the greenstone units. (2) Dn+1 is characterized by a pervasive, southeasterly–dipping Sn+1 foliation that is axial–planar to several asymmetric, tight to isoclinal and recumbent folds. (3) Dn+2 represents a strike–slip NE–trending shear zones, and (4) the late Dn+3 event is characterized by ductile–brittle deformation. Evolution from Dn+1 to Dn+3 is interpreted as a progressive deformation, with the maximum compressive stress in the WNW–ESE direction. The main stage of gold mineralization is associated with the Dn event, and comprised by deformed quartz veins and associated high–temperature calc–silicate alteration (diopside, hornblende, titanite) and albitization of the host rocks. Lower temperature gold (±Te, Ag) occurs along late stage brittle structures (Dn+3). The U–Pb titanite age of 2029 ± 28 Ma for the calc–silicate alteration of the early gold mineralization is similar to the age of many Transamazonian/Eburnean gold mineralizations elsewhere. However, the strong Pb loss of titanite grains defines a 574 ± 7 Ma lower intercept age, indicating that early gold mineralization was affected (remobilized) by Neoproterozoic deformational events and metamorphism (Brasiliano/Pan–African orogeny). This is in agreement with the U–Pb zircon age of 575 ± 3 Ma obtained for the syn–tectonic Guaribas dikes, which bracketed the age of Dn+3. Therefore, as Dn+1, Dn+2 and Dn+3 evolved by progressive deformation; they are all of Neoproterozoic age. This two–stage gold mineralization is here interpreted as product of crustal exhumation, with (1) early hypozonal orogenic gold mineralization occurring shortly after the high–grade Paleoproterozoic metamorphism and first exhumation processes of the greenstone pile; and (2) late gold mineralization occurring at shallow levels (second exhumation process), associated with the Neoproterozoic Brasiliano/Pan–African orogeny. Image 1 • Four deformation events are recognized (Dn, Dn+1, Dn+2, Dn+3). • The main stage of gold mineralization comprises deformed quartz veins. • The U–Pb titanite age of 2029 ± 28 Ma was obtained for early gold mineralization. • Late (c. 580 Ma) gold mineralization is found in brittle–ductile structures. • A two–stage exhumation–driven gold mineralization is the proposed model. [ABSTRACT FROM AUTHOR]

• Gold is associated with a regional shear zone in a Rhyacian greenstone belt. • Gold is associated with quartz veins, calc-silicate alteration and albitization. • Gold precipitated at the late stages of alteration, close to magnetite and tellurides. • Our results suggests an ore-forming fluid sourced by oxidized magmas. At the Archean-Paleoproterozoic Troia Massif, NE Brazil, two major Paleoproterozoic greenstone belts are documented (Algodões and Serra das Pipocas). They share similar lithostratigraphic characteristics with other 2.2–2.1 Ga greenstone belts of the surrounding cratonic domains (e.g. Guiana shield and West Africa craton). Gold mineralization in the Serra das Pipocas greenstone belt is associated with a regional NE-trending shear zone. In the mineralized area (the Pedra Branca gold deposit) the main gold mineralization is found in association with quartz veins, calc–silicate alteration (e.g. diopside, K-feldspar, amphibole, titanite, biotite, pyrite, albite, magnetite ± carbonates) and albitization. Pyrrhotite is commonly found as inclusions in pyrite, and late magnetite replaces pyrite, suggesting progressive oxidation of the ore–forming fluid. Free-milling gold commonly precipitates at the late stages of alteration, in close association with magnetite and tellurides. The main tellurides found are hessite, altaite, sylvanite, calaverite and tellurobismuthite. Two fluid inclusion assemblages were identified from mineralized quartz veins. Assemblage 1 is characterized by pseudo-secondary trails that show the coexistence of CO 2 –rich and low salinity (0–8 wt% NaCl equiv.) CO 2 –H 2 O–NaCl and H 2 O–NaCl inclusions, suggesting formation during phase separation (fluid immiscibility). Assemblage 2 is represented by late secondary low–temperature (Th < 200 °C) H 2 O–NaCl inclusions, probably unrelated to gold mineralization. The δ18O, δD and δ13C values of hydrothermal minerals (quartz, calcite, biotite, hornblende and magnetite) and fluid inclusions are compatible with a magmatic–hydrothermal ore-forming fluid that underwent fluid–rock interaction with the greenstone sequence. The calculated fluid δ18O values range from +8.3 to +11.0‰ (n = 59), fluid δD from −98 to –32‰ (n = 24) and δ13C values of calcite from −6.35 to −9.40‰ (n = 3). Oxygen isotope thermometry for quartz–magnetite pairs yields temperatures from 467 to 526 °C (n = 7, average 503 °C). This probably represents the temperature of gold deposition, because gold is generally associated with magnetite in the ore mineral assemblage. The estimated PT conditions of the gold mineralization range from 467 °C and 1.93 kbar (7 km) to 526 °C and 3.48 kbar (13 km), repectively, and they were obtained from the intersection of isochores with the temperature range derived from the quartz–magnetite isotope geothermometer. This PT range is akin to hypozonal orogenic gold deposits. The association of gold with magnetite and tellurides implies an ore–forming fluid derived from oxidized magmas, similar to those interpreted as 'orogenic oxidized intrusion-related gold deposits' in other Precambrian greenstone belts (e.g. Abitibi and Eastern Goldfields). [ABSTRACT FROM AUTHOR]

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Abstract The origin and significance of the metavolcanic rocks of the Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of the Guyana Shield in Paleoproterozoic times. This work presents new LA-MC-ICPMS U-Pb zircon data and geochemical analyses carried out on metavolcanic rocks of the VNGB. This information was supplemented by petrography, stratigraphic and structural data acquired through geologic mapping and boreholes descriptions. In the Vila Nova region, the VNGB units rest on the Archean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB consists of metabasalts and andesitic metabasalts, covered by an upper metasedimentary domain with subordinate metavolcanic and exhalative chemical rocks. The metavolcanic rocks include metabasalts, meta-andesites, amphibolites and amphibole schists, deformed and elongated according to the regional NW-SE structure. U-Pb zircon data yielded an age of 2154 ± 6 Ma for a meta-andesite of the lower portion of VNGB. One orogenic metamorphism followed by three deformational events were recognized. The D 1 and D 2 events formed the schistosity (S 1), preserved as intrafolial folds (F 2) and the crenulation cleavage (S 2) associated with the development of the oblique shear zones. Two distinct assemblages: 1) garnet, hornblende and biotite, and 2) hornblende, plagioclase and diopside define two distinct metamorphic peaks: M 1 and M 2 with temperatures of 450 and 650 °C, and lithostatic pressure between 4 and 6 kbar. The metabasites comprise geochemical compositions of Fe- and Mg-tholeiites with komatiitic affinity. The first group is enriched in LREE and HFSE. The second group shows MORB-like REE patterns in association with negative Nb, Ti and P anomalies. The observed features indicate that the metavolcanic rocks of the VNGB represent the evolution of back-arc basins and island arcs associated with the Trans-Amazonian Orogeny. These rocks characterize the Rhyacian evolution of the Maroni-Itacaiunas Province in the eastern portion of the Guyana Shield. Graphical abstract Image 1 Highlights • La-ICP-MS U-Pb zircon geochronology data on meta-andesite established a Rhyacian age (2,154 ± 6 Ma) for the magmatism. • The protoliths are tholeiitic basalts and andesites with geochemistry associated with an island arc-back-arc system. • E-MORB, N-MORB and plume type sources were involved in the formation of the volcanic rocks. • The volcanic rocks were affected by metamorphic events under greenschist-amphibolite and hb-px hornfels facies conditions. [ABSTRACT FROM AUTHOR]

The Pequizão gold deposit in the Crixás greenstone belt, central Brazil, is structurally-controlled mineralization hosted mainly in carbonaceous phyllite with pervasive hydrothermalized zones and large amounts of disseminated sulfides and gold. Usually, regoliths of Au deposits are either unstudied or understudied in exploration surveys because of lower Au content and the difficulty and complexity of soil profiles. However, such investigation can be beneficial in brownfield exploration to assess larger areas than drilling. In this work, results of clustering and machine learning of soil geochemistry and reflectance spectroscopy integrated with a multivariate approach to determine soil footprints and to target new deposits in the surface of the Crixás greenstone belt. Reflectance spectroscopy was applied in 939 soil samples and is a valuable tool in mineral exploration for an immediate investigation of mineral assemblage from the target. It was calibrated with X-ray diffraction, geochemical, and multivariate approaches providing consistent vectors toward mineralization, with Pequizão soil samples developing gibbsite and phengitic-white mica as minerals related to mineralized samples. Multivariate analysis reveals that the deposit has a typical orogenic gold deposit chemical signature. Principal components and factor analysis first defined samples derived from carbonaceous phyllite and dolomite as the main ore hosts. The chemical aspects of hydrothermal alteration are As, Ag, Te, Ca, and Mg, with enrichment of Sb, V, Na, Ba, and W and depletion of Zn, Ga, and Pb that, according to ensemble learning, they have significant importance in the detection of gold. Understanding surface footprints of known deposits can be an exploratory guide for finding new soil geochemical halos related to mineralization zones. The research revealed new associations of minerals and chemical elements that can be determined as exploration vectors. It was possible to clarify further the knowledge about the footprint of mineralization in soil. Combining the soil-related methods applied in this study and a broad-coverage spectral approach in soil and drill cores can enhance success in prospecting in brownfield areas and expand to greenfields. • Near-mine soil sampling in different depths at a gold deposit • Hydrothermal alteration signature has gold-associated elements (e.g., Ag, As, Ga, Sb). • Ensemble learning highlighted Zn, Ga, and Pb as important for Au prediction • Mapping of the Principal Component 3 potentially tracks Au and As enrichment. • Soil spectral analysis has muscovite content tending to phengite in gold-rich samples. [ABSTRACT FROM AUTHOR]

Quadrilátero Ferrífero (QF) is a worldwide known metallogenetic province and has in its NW portion the Pitangui greenstone belt, one of the new frontiers for gold exploration in that region, presenting important gold deposits, such as Turmalina and São Sebastião. Among several actions of the geological and mineral resources projects carried out by Geological Survey of Brazil (SGB/CPRM) in the QF region, a high-density geochemical survey (1 sample/4 km2) by stream sediments was accomplished in its NW portion to better understand the behavior and distribution of chemical elements along the main geological units, especially those related to gold mineralization (Au, As, Sb, Bi, etc.). The exploratory data analysis (EDA), regarding uni-, bi-, and multivariate analyses, point to an important chemical control of the stream sediments by the geological units and help to describe some lithological features and to understand the behavior and distribution of hydrothermal processes and gold mineralization. This procedure defined the main geochemical associations, including the association As, Sb, Cu and Bi linked to Ni, Cr and Co, interpreted as gold mineralization hosted in the metavolcanosedimentary lithotypes. The staged factor analysis (SFA) considering compositional data (CoDa), logistic function, and fractal model approaches provided the generation of the geochemical mineralization probability index (GMPI), which produce a GMPI map for gold mineralization. The calculations did not take into account the gold concentrations but only the pathfinder elements and the model validation by the prediction-area plot, confirm the high performance of this approach. The gold mineralization map, in addiction to satisfactorily predicting the location of most known gold occurrences, was able to indicate new potential targets for prospecting new gold deposits. • Geochemical mapping in the new gold mining frontier of Quadrilátero Ferrífero • Robust statistics methods are useful to define and describe geochemical signatures. • Geochemical mineralization probability index defines new gold targets. • This approach presented high performance considering only the pathfinder elements. [ABSTRACT FROM AUTHOR]

Geochemical mapping has become essential to prospective assessments in both brownfield and greenfield exploration targeting. During the last two decades, several techniques have been applied to the identification of mineralization's geochemical signature. Among these techniques, Hierarchical Clustering (HC) and Principal Component Analysis (PCA) have been widely used. Other techniques, like Multifractal Spectrum (MS) and Local Singularity Mapping (LSM), are efficient in the generation of models suitable to determine the type of database statistical distribution and mapping zones of geochemical enrichment and depletion. We combined these techniques for soil and stream sediment geochemistry and generated two prospective geochemical models for the gold deposits from the Pitangui Greenstone Belt (PGB), located at northwest of Quadrilátero Ferrífero – Brazil. The results of PCA and HC showed a geochemical association of As-Bi-Mo-Sb with gold mineralization in the PGB. According with descriptive statistical analysis, these elements do not display normal or log-normal statistical distribution, which allowed the application of multifractal models on the geochemical mapping. MS technique revealed that all elements associated with gold have a multifractal distribution. In addition, geochemistry data shows that high contents of elements measured in the stream sediment analysis displays greater dispersion when compared to elements of soil geochemistry data, due to their mobility in environmental conditions. We used LSM technique to map geochemical enrichment of the elements associated with gold. The maps were evaluated using the Ground Truth Analysis (GTA) and the results showed a good performance in the identification of prospective zones. The anomalies identified in both geochemical maps showed a strong correlation between geochemical enrichment zones and geological factors that favors gold mineralization. These results bring a new perspective on the distribution of geochemical anomalies using, for the first time, the multifractal geochemical modeling on the PGB. The geochemical maps point to new targets for mineral exploration and contribute significantly for the prospective models of the region. [ABSTRACT FROM AUTHOR]

The structural architecture of an orogenic deposit is essential for its metallogenetic understanding, as both subjects are interconnected in this type of environment. Cuiabá gold deposit, located in Archean rocks from Rio das Velhas Greenstone Belt, is the subject of numerous studies focused mainly on metallogenetic issues. From the point of view of structural characterization, two divergent models have been studied: the sheath-fold model and the refolding model. Such hypothesis is different in terms of defining an exploratory research plan and, therefore, the detailed structural characterization is still not well understood. As a way of filling this gap, the main objective of this work is to propose a structural characterization of the entire deposit in order to demonstrate evidence for a new model of tectonic evolution. For this, the methodologies applied for this work were: underground geological mapping in all available ore galleries and definition of geological-structural domains whose main criteria are related to down-plunge view of fold asymmetry and stratigraphic indicators. Structural geology is characterized by 3 deformation phases related to 2 tectonic events. The first event has two ductile-progressive deformation phases (D1 and D2), with NE-SW strike-slip direction of transport associated coaxial fold interference patterns with cylindrical geometry plunging to ESE, which represents the main structure at the mine. The second event is a brittle-ductile deformational phase (D3) with W-verging reverse fault systems, probably associated to Brasiliano Pan-African Orogeny. Gold mineralization is associated with silica and sulfide-rich hydrothermal fluid introduction through D1 and D2 axial-plane foliation. Phase D1 is pyrrhotite-associated mineralization, with coarse gold presence. D2 phase has pyrite-associated mineralization with fine gold. There is no gold in phase D3, although it has late-tectonic sulphides formation. Therefore, there is no field evidence that corroborate the existence of sheath folds for the deposit. Fold interference patterns associated to deposit morphology suggests SW and N prospective targets, with strong possibility of structural connection between other gold deposits, such as Lamego and Descoberto targets. • Geological mapping reveals a pre-Cambrian fold interference pattern with no field evidence for sheath folds. • Gold inside BIF is related to this framework at two stages: (1) pyrrhotite with coarse gold and (2) pyrite with fine gold. • A NE-SW ductile strike-slip transport at a convergent tectonic setting with inclined folds plunging to ESE is suggested. • Gold was carried out throughout axial-plane foliation and were placed where coaxial refolding was locally presented. • A post-mineralization tectonic event was responsible for orthogonal displacements at the entire deposit. [ABSTRACT FROM AUTHOR]

Potential-field edge detection filters are powerful fault detection tools in mineral exploration. The application of these filters to electromagnetic (EM) data is not as accepted as those associated with potential field data. But they may be advantageous when dealing with mineralizations associated with non-magnetic rocks. This paper introduces the multiscale edge detection filter to provide an enhanced image of fault zones when applied to apparent conductivity data. The Rio das Velhas Greenstone Belt, the studied area, hosts several gold mineralizations controlled by northwest–southeast shear zones subparallel to non-magnetic metasedimentary rocks that are typical candidates for the EM interpretation. Several northwest–southeast trending faults were highlighted in the studied area. We employed a data fusion interpretation strategy by correlating the detected EM faults with radiometric anomalies to classify high-priority spots for future exploration. We tagged four known gold deposits and new targets with similar characteristics following the proposed guidelines. • We show that the multiscale filter (worming) can be used for electromagnetic (EM) data. • The EM worming screened non-magnetic mineralized fault zones in the Rio das Velhas Greenstone Belt. • Combining EM-worming and radiometric data, we selected sites for follow-up surveys. [ABSTRACT FROM AUTHOR]

Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. Outcrops of spinifex-textured komatiites, located ∼1.5 km to the south of the Carajás ridge, were discovered during regional exploration for Ni–Cu–(PGE) sulfide deposits by VALE. They are associated with a 3.8 km long unit consisting of variable types of ultramafic rocks (talc schist, serpentinite and spinifex-textured komatiite). This ultramafic unit follows the steep dipping NW–SE trending Selva greenstone belt composed mainly by quartz-chlorite schists (interpreted as metasediments) and chlorite-actinolite schists (interpreted as metabasalts). Greenschist facies metamorphic parageneses characterize all rock types in the Selva greenstone belt. The komatiitic rocks in the Selva belt comprise a sequence of flows consisting of an upper spinifex-textured layer and a lower olivine cumulate layer. Although the spinifex and cumulus textures are well preserved in the field, the primary mineralogy of the komatiites has been completely replaced by greenschist facies metamorphic minerals. Platy olivine spinifex texture, consisting of an array of roughly parallel olivine plates, and random spinifex texture, consisting of randomly oriented olivine plates, are the most common primary volcanic textures in komatiites in the Selva greenstone belt. Platy and random spinifex texture is defined by former plates of olivine replaced by serpentine with minor actinolite, chlorite and magnetite, alternating with former matrix replaced by abundant actinolite and minor chlorite, talc, serpentine, and magnetite. The domains between olivine plates in both platy and random spinifex-textured rocks contain irregular arrays of fine-grained parallel crystals, representing primary fine-grained “quench” clinopyroxene crystals replaced by actinolite. Spinifex-textured komatiites have MgO contents bracket between 22.8 and 26.9 wt.%, and cumulate textured komatiites have MgO contents up to 40.6 wt.%. When plotted vs MgO contents, most major and minor elements fall on well-defined linear trends indicating control by olivine fractionation or accumulation. Komatiites from the Selva and Seringa (located in the Rio Maria Domain) belts are Al-undepleted with Al 2 O 3 /TiO 2 ratios close to 20. Results for CaO, Na 2 O, and REE suggest that these elements were mobile and their abundances have been modified during metasomatic alteration. REE contents in some samples are very high (up to 40 times primitive mantle values) and REE patterns vary from flat (La/Yb MN ∼ 1) to highly enriched in LREE (La/Yb MN up to ∼ 10). The REE mobility may be related to hydrothermal alteration associated to Cu–Au mineralization in the region. The identification of spinifex-textured komatiites close to the Carajás Basin suggests the continuation of 3.0–2.9 Ga greenstone belts of the Rio Maria Domain within the Transition Subdomain, and enlarges the area with potential to host komatiite-associated Ni–Cu–PGE deposits. [ABSTRACT FROM AUTHOR]

Archean orogenic gold deposits are hosted in the Rio das Velhas greenstone belt in the eastern sector of the Quadrilátero Ferrífero, Southern São Francisco Craton region, southeastern Brazil. These include the gold deposits along the NE-trending Córrego do Sítio lineament, stretching for some 15 km, and the Pilar deposit, object of the present study. These deposits occur in an area close to the boundary of the São Francisco craton, which is commonly interpreted to have preserved the Archean and Paleoproterozoic crust from the effects of Ediacaran-Cambrian Araçuaí orogenic front. The gold deposits were formerly interpreted as exclusively Archean (ca. 2.7 Ga). However, recent geochronological data suggest the imprint of the late Ediacaran-Cambrian Brasiliano Orogeny in host rocks of these deposits, as structural modification or hydrothermal alteration assemblages that postdates Archean mineralization. To elucidate those issues, contextual (thin section) in-situ U–Pb SHRIMP dating was conducted on hydrothermal monazite crystals from the Carvoaria and Cachorro Bravo deposits of the Córrego do Sítio lineament and from the Pilar gold deposit. Hydrothermal monazite in mineralized metapelites from Carvoaria yielded a U–Pb Discordia with intercepts at 2,514 ± 22 Ma and 555 ± 19 Ma. Three younger, age-equivalent crystals are concordant and yielded a U–Pb Concordia age of 539 ± 9 Ma, identical within uncertainties to the lower intercept age. Monazite from the Cachorro Bravo deposit yielded U–Pb Concordia ages of 551 ± 10 Ma and 510 ± 11 Ma. Monazite from the veined (silicified) sulfide-schist from the Pilar deposit is depleted in U, precluding the calculation of robust U–Pb ages, and disclosed a mean 208Pb/232Th average age of 508.2 ± 6.4 Ma. These results reinforce the proposal of a strong Ediacaran-Cambrian imprint related to the final stages of the Brasiliano orogenic event, affecting Archean gold deposits throughout the Quadrilátero Ferrífero. Consequently, the results point to the importance of mapping Brasiliano-related structures that control the spatial arrangement of the gold deposits, such as the Córrego do Sítio lineament, consisting of an important exploration target. This major NE-SW trending strike-slip shear zone hosts several gold deposits and might represent an Archean structure reactivated during the Brasiliano Orogeny that possibly led the large volume of Ediacaran-Cambrian post-collisional hydrothermal fluids among the east sector of the Quadrilátero Ferrífero. • U–Pb SHRIMP dating of gold-related hydrothermal monazite on thin section. • Cambrian ages indicate resetting of the Archean mineralization by fluid flow. • Influence of the Brasiliano Araçuaí Orogen over the São Francisco Craton border. [ABSTRACT FROM AUTHOR]

The Pitangui Greenstone Belt (PGB) is a Meso to Neoarchean metavolcano-sedimentary sequence, inserted in the Pitangui Synclinorium, located in the northwest portion of the Archean-Paleoproterozoic metallogenic province of the Quadrilátero Ferrífero, southern of the São Francisco craton (Brazil). The PGB holds important gold mines like the Turmalina Complex and recently discovered deposits, as São Sebastião. The PGB is mapped in detail scale, but there is still little information about its subsurface configuration. This paper presents gravity surveys, constrained by geological, structural, boreholes, aeromagnetic and seismic data, aiming to provide a better understanding of the 3D geometry of this granite-greenstone terrane. The treatment of the available data resulted in Bouguer anomaly maps, 2D gravity modelling and a 3D geological-geophysical integrated model. The gravity Bouguer anomalies of the region present high amplitudes associated with the PGB, alternating with low zones related to the surrounding granite-gneiss rocks. The profiles and the model suggest that the maximum depth of the greenstone belt is approximately 5 km in its central portion, being strangled by granitic intrusions in its southernmost region. The PGB is about 100 km long, but most of it is covered by Neoproterozoic sediments of the Bambuí Group and Quaternary deposits, which significantly increase its metallogenic potential, especially in regions with few mineral exploration works. The 3D model contributes to the understanding of the tectonic framework and evolution of the PGB, showing the spatial relation with the surrounding granite-gneiss basement and intrusions, and younger sedimentary covers, providing valuable insights about their depth, vertical and lateral geometry. Additionally, this new data can become a valuable tool for developing strategies to select deep mineral targets, expanding the exploratory potential for this mineral province. • Pitangui greenstone belt present high amplitude Bouguer anomaly. • The greenstone belt extends in a much larger area than it outcrops. • The greenstone belt has 5 km depth on the central portion. • 3D model present the geometry of this granite-greenstone terrane. [ABSTRACT FROM AUTHOR]

The goal of this work is to emulate a situation where an analyst with none or little previous geological knowledge of the samples must deal with an unsupervised approach to gain some insights about drill core samples and compare the results of two main unsupervised algorithms with and without filtering methods. We used in situ portable X-ray Fluorescence data acquired in sawn drill core samples of rocks from the Sabiá prospect, at the Rio Salitre greenstone belt, São Francisco Craton Brazil, for pseudo-log automatic generation through running Unsupervised Learning models to group distinct lithotypes. We tested the K-means and Model-Based Cluster (MBC) algorithms and compared their performance in the raw and filtered data with a manual macroscopic log description. From the initial 47 available elements, 20 variables were selected for modeling following the criteria of presenting at least 95% of uncensored values. Additionally, we performed a Shapiro-Wilk test that confirmed a non-parametric distribution by verifying the P-value attribute less than the 5% significance level. We also checked if the dataset's distribution was statistically equivalent to the duplicates with the assistance of a Kruskal–Wallis test, which would confirm the representativity power of the measurements at the same 5% significance level. After this step, the pseudo-log models were created based on reduced dimension data, compressed by a centered Principal Component Analysis with data rescaled by its range. Concerning reducing the high-frequency noise in the selected features, we employed an exponential weighted moving average filter with a window of five samples. By the analysis of the Average Silhouette Width on sample space, the optimum number for K-means was fixed in two, and then the first models were generated for raw and filtered data. From the MBC perspective, the sample space is interpreted as a finite mixture of groups with distinct Gaussian probability distribution. The number of clusters is defined by the analysis of the Bayesian Information Criteria (BIC), where several models are tested, and the one in the first local maximum defines the number of groups and the type of probabilistic model in the simulation. For the data used in this work, the optimum group number for MBC is four, and the probabilistic model type determined by the BIC is elliptical with equal volume, shape, and orientation. Thus, Model-Based Cluster has detected four different cluster groups with almost the same representativity for the two drill cores' samples. All K-means and MBC models were able to detect changes in lithotypes not described in the manual log. On the other hand, one lithotype described by the experts was not detected by this methodology in any attempt. It was needed a detailed investigation with thin section descriptions to determine the cause of this response. Finally, compared with the manual log description, it is notable that the models built on filtered data have better performance than those generated on raw data, and the MBC filtered model had better performance than the others. Hence, this multivariate approach allied to filtering the data with a moving average transformation can be a tool of great help during several stages of mineral exploration, either in the creation of pseudo-log models prior the description of the drill core samples or in the data validation stage, when it is necessary to standardize several descriptions made by different professionals. • The filtering process enhanced the geochemical contrast when compared to raw data. • Pseudo-log generation takes benefit from filtering and PCA process. • Both Clustering methods used were able to detect significant differences in lithotypes. • MBC models are closer to the manual log description than K-mean results. [ABSTRACT FROM AUTHOR]

The 642 Ma-old Brauna Kimberlite Field is located on the northeastern sector of the São Francisco Craton (Serrinha block) and is one of the rare Neoproterozoic kimberlitic events in South America. Zircon xenocrysts from the volumetric most important kimberlite pipes Brauna 03, Brauna 07 and Brauna 04 were used as a tool to identify different components of the lithosphere beneath the northeast region of the São Francisco craton. A composite kimberlite sample of eight representative and different drill holes and three samples of the host rocks (Nordestina granodiorite) were sampled for SHRIMP geochronology. The results were compared with precise U–Pb age data for the regional rocks, i.e. the Archaean basement and the Palaeoproterozoic Rio Itapicuru greenstone belt. Samples from the Nordestina granodiorite gave three different ages: 2155 Ma in the western part of the batholith, 2139 Ma in its central part, and 2132 Ma in its eastern part. Zircon 207Pb/206Pb ages of the Brauna kimberlite zircon grains spread over the timespan 2107–2223 Ma and indicate four age groups at 2105 ± 3 Ma, 2138 ± 7 Ma, 2166 ± 5 Ma, and 2198 ± 4 Ma. Source rocks for the three former age groups can be found in the Rio Itapicuru greenstone belt, including zircon xenocrysts from the Nordestina granodiorite, whereas the latter age group has not yet been reported in the Serrinha block. The new zircon ages show that only rocks of the Palaeoproterozoic Rio Itapicuru greenstone belt and of a hidden 2.17–2.20 Ga crust were sampled by the kimberlite magma during its ascent through the lithosphere. It is proposed that there is none or a few Archaean crust beneath the kimberlite emplacement area, hence implying a thick Palaeoproterozoic lithosphere for this portion of the São Francisco craton. [ABSTRACT FROM AUTHOR]

Central Amapá, northern Brazil is located at the boundary between: (a) a northern Paleoproterozoic domain, consisting mainly of granite-greenstones terrains and (b) a southern Archean continental block (Amapá block), including an Archean basement reworked during the Transamazonian orogeny (2.26–1.95 Ga). Field investigations, Pb–Pb zircon and Sm–Nd whole rock geochronology supported by geochemical data on granitoids brought further constraints on Paleoproterozoic crustal growth in the southeastern Guyana Shield. A first magmatic episode, dated at 2.26 Ga, is marked by the crystallization of metaluminous low-K tholeiitic tonalites and quartz-diorites, which geochemical affinity with volcanic arc and association with T-MORB amphibolites suggest that they formed in a back-arc basin – island arc system. This event is coeval to the oceanic stage registered in French Guyana during the Eorhyacian (2.26–2.02 Ga). A second magmatic episode is represented by peraluminous, medium- to high-K calc-alkaline tonalite and granodiorite, which revealed some similarities with Mesorhyacian TTG rocks of French Guyana. For granitoids of both episodes, TDM and εNd values indicate the contribution of some Archean crustal component, probably by assimilation or contamination. This second magmatic episode occurred at 2.10 Ga, indicating that the period of successive calc-alkaline magmatic arcs formation may have extended until the Neorhyacian. Meanwhile, during this time, tectonic accretion by collision of the newly formed continental landmass was the prevailing process in French Guyana. The latter magmatic episode, even though poorly constrained, was registered around 2.08–2.02 Ga in central Amapá. It corresponds to the emplacement and solidification of high-K collisional granitoids, produced by partial melting of the Archean continental crust, as testified by the Archean TDM, inherited Pb–Pb zircon ages and strongly negative εNd values. Our results point toward the existence of a protracted episode of crustal growth during the Neorhyacian in the southeastern Guyana Shield. This episode has been predominantly driven by magmatic arc accretion during, at least, 160 My, along the period of 2.26–2.10 Ga. This cycle ended with diachronic closure of the oceanic basins and arc–continent collision. [ABSTRACT FROM AUTHOR]

Abstract: A study of sediment provenance and tectonic setting was carried out for the first time on metasedimentary rocks of the Rio Itapicuru greenstone belt, Serrinha Block, São Francisco craton, Brazil, using a combination of LA-ICP-MS zircon U–Pb geochronology, whole-rock geochemistry and Sm–Nd isotope data. The protoliths of the studied phyllites, micaschists and biotite gneisses were classified mostly as mudstones and impure sandstones, i.e. shales and greywackes. The chemical index of alteration (CIA) ranges from 39 to 70 indicating moderate chemical weathering in source areas. Intermediate and felsic rocks (granite, granodiorite, rhyolite and andesite) are the likely main source rocks, and less often mafic rocks (basalt and gabbro). The depleted-mantle Nd model ages (T DM), most in the range 2.0–2.2Ga, and the positive ɛ Nd values for the proposed deposition time (ca. 2115Ma) suggest source rocks mainly in the greenstone belt. The U–Pb data on detrital zircon grains of four samples yielded 207Pb/206Pb age mostly in the timespan 2125–2237Ma, with age populations clustering at 2164 ± 4Ma and 2209 ± 4Ma, and minor outliers at ca. 2112Ma, 2270Ma, and 2415Ma. The results indicated that the metasedimentary rocks of the Rio Itapicuru greenstone belt have source areas mainly in Palaeoproteroic terranes such as the Rio Itapicuru and Rio Capim greenstone belts. The zircon populations between 2.17Ga and 2.24Ga are not found in the Serrinha block, thus requiring sources that are not known in the region. Diagrams of tectonic setting suggest that the sediments may have been deposited on continental island arc. Our data support a model in which basalts and arc granites of the Rio Itapicuru greenstone belt were accreted onto an unknown continental or arc margin and the entire pile collided with, and were thrust onto a microcontinent represented by the adjacent Archaean basement complex. [Copyright &y& Elsevier]

Abstract: Several granitic plutons have intruded the Palaeoproterozoic Rio Itapicuru greenstone belt, São Francisco craton, Brazil, in the time interval 2163-2080 Ma, but their tectonic significance is poorly understood. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with Archaean migmatite-gneiss basement. The pluton is mostly composed of hornblende granodiorite, occasionally crosscut by syn-plutonic mafic dykes. The FGG is metaluminous, medium- to high-K calc-alkaline with relatively constant silica abundances (SiO2 ∼ 63–66 wt%), high Sr (900–800 ppm) and high Ba (1000–1500 ppm). The associated mafic dykes are ultrapotassic, with high abundances of Ba, Sr, MgO, Ni, Cr, and light rare earth elements, suggesting derivation from partial melts of an enriched mantle source. The FGG originated probably by fractional crystallization from a primitive K-rich mafic magma that interacted with crustal melts. Its zircon U–Pb SHRIMP age of 2106 ± 6 Ma indicates that the FGG is younger than the early (2163-2127 Ma) tonalite-trondhjemite-granodiorite (TTG) and calc-alkaline arc plutons of the greenstone belt, and is closely related in time and space with potassic to ultrapotassic plutons (ca. 2110-2105 Ma). The negative εNd(t) of FGG and coeval K-rich plutons of the Rio Itapicuru greenstone belt contrasts markedly with the positive εNd(t) of the older arc plutons, indicating a major change of isotope signatures in granites of the Rio Itapicuru greenstone belt with time. This isotope shift may be related to magma contamination with older continental material and/or derivation of the parental potassic magma from enriched lithospheric mantle sources. We suggest that the K-rich plutons were emplaced during or shortly after Palaeoproterozoic arc-continent collision. [Copyright &y& Elsevier]

Abstract: The Crixás greenstone belt, Central Brazil, consists of a greenschist to low amphibolite facies metamorphic volcanosedimentary sequence that contains the sixth largest gold reserve (∼70t Au, in the average 12g/t) of Brazil and the largest gold-only deposit of Central Brazil. The gold orebodies are hosted by low-angle thrust faults within the stratigraphically upper metasedimentary rocks and are crosscut by a set of post-mineralization mafic dykes. For decades the sequence has been interpreted as a typical Archean greenstone belt of the Brazilian Shield and the gold mineralization considered either Archean or Neoproterozoic. This study shows the results of in situ U–Pb SHRIMP and LA-ICP-MS dating of detrital zircon grains from graywacke and mafic dyke samples, as well as Pb and Nd isotopic signatures of the ores. The oldest detrital zircon grains of the graywacke samples yielded U–Pb ages of 3354±40Ma and the youngest between 2209±28Ma and 2222±30Ma, which indicates a mixture of Archean and Paleoproterozoic (Rhyacian) source area and that the maximum depositional age is of ca. 2.2Ga. Magmatic zircon of the post-mineralization mafic dykes yielded the U–Pb age of 2170±17Ma, which suggests that the basin stage, its deformation, metamorphism and mineralization were restricted to the Rhyacian and took place during a time-span of about 30–40m.y. The paper thus provides a new insight into the age of the Crixás greenstone belt rocks and of its gold-only deposits, and reveals that Mid-Paleoproterozoic was a more widespread metallogenetic epoch related to greenstone belts of the Brazilian Precambrian Platform then previously interpreted. The observed Pb and Nd isotopic signatures of the ores suggest that metabasalts, carbonaceous schist and metagraywackes could provide the adequate sources for the ore-bodies and that the initiation of fluid circulation may have resulted by the emplacement of a high-level granite. [Copyright &y& Elsevier]

Abstract: U–Pb single zircon crystallization ages were determined using TIMS and sensitive high resolution ion microprobe (SHRIMP) on samples of granitoid rocks exposed in the Serrinha nucleus granite–greenstone terrane, in NE Brazil. Our data show that the granitoid plutons can be divided into three distinct groups. Group 1 consists of Mesoarchaean (3.2–2.9Ga) gneisses and N-S elongated TTG (Tonalite-Trondhjemite-Granodiorite) plutons with gneissic borders. Group 2 is represented by ca. 2.15Ga pretectonic calc-alkaline plutons that are less deformed than group 1. Group 3 is ca. 2.11–2.07Ga, late to post-tectonic plutons (shoshonite, syenite, K-rich granite and lamprophyre). Groups 2 and 3 are associated with the Transamazonian orogeny. Xenocryst ages of 3.6Ga, the oldest zircon yet recorded within the São Francisco craton, are found in the group 3 Euclides shoshonite within the Uauá complex and in the group 2 Quijingue trondhjemite, indicating the presence of Paleoarchaean sialic basement. Group 1 gneiss-migmatitic rocks (ca. 3200Ma) of the Uauá complex constitute the oldest known unit. Shortly afterwards, partial melting of mafic material produced a medium-K calc-alkaline melt, the younger Santa Luz complex (ca. 3100Ma) to the south. Subsequent TTG melts intruded in different phases now exposed as N-S elongated plutons such as Ambrósio (3162±26Ma), Araci (3072±2Ma), Requeijão (2989±11Ma) and others, which together form a major part of the Archaean nucleus. Some of these plutons have what appear to be intrusive, but are probably remobilized, contacts with the Transamazonian Itapicuru greenstone belt. The older gneissic rocks occur as enclaves within younger Archaean plutons. Thus, serial additions of juvenile material over a period of several hundred m.y. led to the formation of a stable micro-continent by 2.9Ga. Evidence for Neoarchaean activity is found in the inheritance pattern of only one sample, the group 2 Euclides pluton. Group 2 granitoid plutons were emplaced at 2.16–2.13Ga in a continental arc environment floored by Mesoarchaean crust. These plutons were subsequently deformed and intruded by late to post-tectonic group 3 alkaline plutons. This period of Transamazonian orogeny can be explained as a consequence of ocean closure followed by collision and slab break-off. The only subsequent magmatism was kimberlitic, probably emplaced during the Neoproterozoic Braziliano event, which sampled older zircon from the basement. [Copyright &y& Elsevier]

The Mamão gold deposit, located in the eastern portion of the Amazonian Craton, northern Brazil, is hosted by mafic rocks of the Mesoarchean Andorinhas greenstone belt. An underground mine was operated in this area by Troy Resources Ltd., which produced approximately 350 koz of gold between 2008 and 2015. The hydrothermal alteration halos are characterized by a distal zone (10- to 80 m wide) with a chlorite-albite-epidote-actinolite assemblage, an intermediate zone (5- to 20 m wide) marked by calcite-albite-chlorite-actinolite-quartz, a proximal zone (0.5–5 m wide) composed of biotite-quartz-calcite-pyrite-(gold) and a quartz vein-hosted orebody zone (0.5- to 6 m wide) composed by quartz-calcite-pyrite-(gold). Geochemical data indicate that the metabasalt, metandesite and metadacite host rocks display a tholeiitic N-MORB signature, suggesting that they were formed in ancient oceanic spreading centers. Hydrothermal chlorite of the Mamão deposit is classified as ripidolite and brunsvigite. Biotite is the main mica and increases in modal content from the distal alteration to the vein zone, displaying compositions within the annite domain. Muscovite occurs as very fine lamellae and is generally located in the intermediate zone of the altered region. Amphiboles are calcium-rich and display compositions mostly varying from hornblende (Mg-hornblende to Fe-hornblende) in the distal zone, to actinolite in the intermediate zone. Sulfidation occurs in all hydrothermal alteration zones, with both fine- and coarse-grained pyrite as the main sulfide phase, and lesser amounts of chalcopyrite, pyrrhotite, cobaltite and sphalerite. Fine-grained pyrite contains many gold inclusions and is typical of the orebody zone preferentially in close contact with the proximal hydrothermal zone, whereas coarse-grained pyrite (without recoverable gold) occurs in the veins. From the edges to the core of the hydrothermal alteration halos, the As, Sb, Ag and Au contents in the pyrite increase, whereas Pb, Co and Mo decrease. Gold occurs as free crystals (2- to 0.1 mm) disseminated within the gangue or as inclusions in the fine-grained pyrite. Temperature estimated via chlorite geothermometer ranges from 284- to 320 °C, with pressure between 1.12 and 1.34 kbar according to biotite geobarometer calculations for the hydrothermal zones. The C–O–S isotope analyses of the calcite and pyrite from the orebody zone yielded δ13C, δ18O and δ34S values ranging from −4.23 to −3.54‰, 8.60–9.77‰ and 3.37–3.52‰ respectively, which suggests that the hydrothermal fluid is predominantly of metamorphic origin. The εNd (3.0) calculated using isotopic analyses of the metavolcanic host rocks varies between +0.11 and + 4.25. A whole-rock Sm–Nd isochron age of 2952 ± 14 Ma was obtained from the host rocks, while a post-mineralized pyrite yielded a Sm–Nd isochron age of 2446 ± 35 Ma. The deposit exhibits mineralogical and isotopic characteristics consistent with those of orogenic type containing gold-bearing, sulfide-rich quartz veins. The Mamão deposit's host rocks are among the oldest rocks described so far in the Carajás Province. The age of the mineralizing event is limited between 2.95 and 2.45 Ga (probably ca. 2.7 Ga), which is the major metallogenic event of gold-deposit formation in several granite-greenstone terrains worldwide. [Display omitted] • Characterization of hydrothermal alteration halos. • Geochemistry and mineral chemistry of hydrothermal alteration minerals. • P-T conditions and source of hydrothermal fluid. • Sm–Nd and C–O–S isotopes of orogenic gold deposit. • Archean gold deposit in the Amazonian Craton. [ABSTRACT FROM AUTHOR]

The Archean-Paleoproterozoic Crixás greenstone belt is one of the most important components of the Crixás-Goiás Domain, the oldest crustal segment of the Central Brazil Goiás Massif. This gold-bearing greenstone comprises amphibolite facies ultramafic-mafic metavolcanic rocks overlaid by a low-grade metasedimentary succession associated with rocks of intermediate composition. We present new integrated geochemical and isotopic data of the metaigneous rocks to characterize the stages of magmatism and delineate the petrogenetic processes and tectonic environment of the different units. The data give important insights into the geological evolution of the Crixás greenstone belt during the Archean and Paleoproterozoic, including that the Crixás greenstone belt consists of genetically and temporal unrelated rocks that are spatially associated in a structural framework marked by stacking and imbrication. Two lithological assemblies were described: i) a Mesoarchean komatiite-tholeiite association formed by heterogeneous mantle plume melting in an oceanic plateau setting, and ii) a Rhyacian intraoceanic arc association. These units are allochthonous and override an Archean crustal basement dominated by granites and gneisses of mostly TTG composition. Chemical composition of the komatiites is similar to the Barberton-type Al-depleted komatiites, whilst the basalts consist of high-Mg tholeiites with flat chondrite-normalized REE patterns and immobile trace element systematics that resemble Phanerozoic oceanic plateau lavas. Eruption age of the ultramafic and mafic lavas is roughly estimated at ~3.0 Ga, based on previously published Sm Nd and Pb Pb isotopic studies, whereas whole-rock Re Os isotopic data of samples of komatiite and basalt presented here yielded a 2609 ± 65 Ma isochron age. This younger age may reflect a Neoarchean overprinting event associated with metasomatic Re-addition recorded in the lower ultramafic-mafic metavolcanic rocks, possibly related to the late stages of the cratonization of the Crixás-Goiás Domain during the emplacement of the youngest Archean granites of the region (~2.70 Ga). Newly described andesites and diorites possess a subduction zone fingerprint. LA-ICP-MS U Pb zircon dating of an andesite sample provided an upper intercept Concordia age of 2172.2 ± 12.7 Ma, constraining the age of the intermediate magmatism. Therefore, these rocks are correlated with the Rhyacian syn -orogenic poorly-sorted graywackes and carbonaceous phyllites of the greenstone's upper stratigraphy. Andesites and diorites have homogeneous Paleoproterozoic two-stage Nd model ages of 2.28 to 2.26 Ga and positive initial εNd values of +2.34 to +2.69, indicating a juvenile nature for the arc magmatism. Re Os geochronology of gold-related arsenopyrite from a metasedimentary rock-hosted massive sulfide provided an age of 2137 ± 11 Ma, suggesting that the mineralization is also coeval to the Rhyacian collisional stage. • Two distinct assemblies of metaigneous rocks in the Crixás greenstone belt • Archean Al-depleted komatiites and tholeiites formed in an oceanic plateau setting. • Rhyacian (2.17 Ga) intermediate rocks formed in an intraoceanic arc setting. • Gold mineralization is related to the Rhyacian period. [ABSTRACT FROM AUTHOR]

Orogenic Au deposits represent one of the largest sources of gold in the world and in Brazil, particularly at the Quadrilátero Ferrífero, southeastern portion of the São Francisco Craton. In the last decades, advances in in-situ analytical techniques allowed a detailed investigation of the chemistry of sulfides. This can reveal information about the origin and composition of the mineralizing fluids, potential sources of metals and sulfur and the fluid-rock interaction during the ore-forming processes. In this paper we combine Electron Microprobe Analysis and LA-ICP-MS analyses to put constraints on the nature and evolution of the Pitangui gold deposit. The Pitangui deposit represents an important Orogenic Au deposit hosted in clastic metasedimentary rocks of the Pitangui greenstone belt, northwestern portion of the Quadrilátero Ferrífero. Detailed drill hole, petrographic observations and in-situ chemical analyses of the hydrothermal alteration zones show that pyrite is the dominant ore mineral in the deposit and two possible origins are suggest including (i) syngenetic pyrite development at the early stages of the greenstone belt evolution and (ii) epigenetic pyrite, which is associated with hydrothermal processes during the Orogenic Au event. Syngenetic pyrite (PyI) has high Co, Bi, Pb, Sb, Te, Se, Ag and Au concentrations. The PyI could represent an important source of metals, a set of trace elements and likely sulfur for the later Orogenic Au mineralization. Epigenetic pyrites (PyII, PyIII and PyIV), conversely, are mainly found in association with hydrothermal minerals and within the mineralized carbonate-quartz-vein. The variations at Co, Ni, Pb, Te, Sn, Se, As, Bi, Sb, Ag, Mo and W in the epigenetic pyrite indicate that the dehydration PGB sequences during orogenesis constitutes the main fluids sources. The PyV, in turn, only appears at metamafic dyke, but its origin remains unclear. • The Pitangui Orogenic Au deposit records a complex metallogenetic evolution. • In-situ EPMA and LA-ICP-MS trace elements geochemistry can reveal the ore-forming processes. • Syngenetic and epigenetic sulfides display different trace elements composition and suggest different origins. [ABSTRACT FROM AUTHOR]

The Brazilian Pilar and Três Buracos Paleoproterozoic mid-tier gold deposits are located in the south western Pilar de Goiás greenstone belt, containing 61,688 kg and 7,144 kg of gold, respectively, in addition to approximately 30,000 kg of past production (1736–2018). This research aimed to assess the hypothesis that the mobility of alkali elements may be used to facilitate the discovery of new gold deposits in hydrothermal systems by creating geochemical vectors based on alkali element mobility. The hypothesis was first proposed for the mafic rocks in the West Australian Goldfields and has been adopted in other deposits worldwide (E.g., Andorinhas greenstone belt, Brazil, Pataz gold field, Peru, and Rio das Velhas gold deposit, Brazil). The procedures consisted in the analysis of metasedimentary and mafic rock types from two drill holes from the Pilar de Goiás greenstone belt, central Brazil. These drill holes have intercepted mineralized and barren rock types. The petrographic and energy dispersive spectrometric results indicated that the host rocks around the orebodies present intense sericitization, albitization, and sulfidation. The chemical results reveal that the mobile elements Cs, Rb and Ba tend to be enriched in gold-bearing rock units and depleted in barren rock units. These elements are carried by fluids and can replace K in the structure of the newly formed hydrothermal phyllosilicates forming a halo of alkali-rich elements of up to 50 m around the orebodies. The upper continental crust normalized ratio ((Cs + Rb)/Th) UCC was adopted as an alteration index to evaluate and distinguish possible mineralized zones, with ((Cs + Rb)/Th) UCC > 3, from barren zones, with ((Cs + Rb)/Th) UCC < 3. The ratio ((Cs + Rb)/Th) UCC increases towards mineralization, providing a vector to possible gold mineralization, with a threshold value > 3 indicating high prospectivity. • 3D lithological model of Três Buracos deposit, central Brazil • Hydrothermal alteration associated with gold-bearing quartz‑carbonate veins • Progressive increase of alkali elements towards gold mineralization. • ((Cs + Rb)/Th) UCC as an exploration vector to find new prospects [ABSTRACT FROM AUTHOR]

The Archean nucleus of the Amazonian Craton, represented by the Carajás Mineral Province (northern Brazil), crops out as a broad exposition of igneous, sedimentary, and metamorphic rocks showing a complex polyphase geologic history. A succession of orthogneisses (metagranitoids), amphibolites, and metavolcano-sedimentary rocks that show greenstone belt characteristics occur in Tancredo Neves Village district, northeast of São Félix do Xingu city (state of Pará), is the focus of this study. Detailed field, petrographic, and stratigraphic data reveal that these metamorphic rocks underwent two different tectono-metamorphic events: (i) the regional metamorphism (>2.8 Ga), which occurred under greenschist-to mid-upper amphibolite-facies conditions; and (ii) the dynamic metamorphism (>2.6 Ga) which reached amphibolite-facies conditions and overprinted previous metamorphic textures. Associated regional strike-slip NW–SE to EW-trending ductile shear zones generated mylonitic, ultra-mylonitic, and migmatitic zones. Whole-rock geochemistry discriminates four groups of metagranitoid protoliths. G1 group is composed of peraluminous trondhjemitic rocks samples, calc-alkaline, weakly fractionated, and enriched in HREE. G2 group comprises metaluminous and alkaline monzogranite samples with high Zr, Y, Nd, HREE, and intermediate fractionation. U–Pb (LA-MC-ICP-MS) dating of G2 zircons yields a crystallization age of 2745.6 ± 5.0 Ma. Groups G3 and G4 encompass peraluminous, calc-alkaline to alkali-calcic, anorogenic, fractionated monzogranitic and granodioritic rocks. G3 and G4 groups are further distinguished by high and low La/Yb (N) ratios, respectively. The results obtained for Tancredo Neves Village district very much resemble the Canaã dos Carajás (Carajás Mineral Province) area characteristics, comprising intense magmatism (2.7–3.0 Ga) and reworking related to at least two distinct metamorphic events in the Archean. As Canaã dos Carajás, Tancredo Neves Village can be a promising area for mining exploration. • Comprises the Archean rocks from the Tancredo Neves Village region, northern Brazil. • Geological, petrographical, and geocronological data for mylonitic gneissic granitoids. • Definition of a regional large-scale metamorphic event transposed by a dynamic event. • Petrogenetic features and comparisons with the easternmost Carajás Mineral Province. [ABSTRACT FROM AUTHOR]

Abstract: The Quadrilátero Ferrífero is a classic gold province on a global scale, with hundreds of individual gold occurrences in the Archean greenstone belt comprising the Rio das Velhas Supergroup. There are numerous small gold deposits, including Faria, Esperança III, Bicalho, Bela Fama, Juca Vieira, Brumal, Boa Vista, Fernandes, Moita, Roça Grande, Bico de Pedra and Pari, as well as the world-class deposits of Morro Velho and Cuiabá. All these deposits, whether large or small, are structurally controlled and related to either shear zones or folds. Extensive down-plunge continuity is a consistent feature of the deposits. In the Rio das Velhas greenstone belt, six main styles of gold mineralization are recognized. These are deposits hosted within: (1), Lapa seca (e.g., Morro Velho, Bicalho, Bela Fama), (2), Banded iron formations (e.g., Cuiabá, São Bento, Raposos, Faria, Brumal, Roça Grande), (3), Quartz veins (e.g., Juca Vieira, Fernandes), (4), Disseminated sulfides with quartz veinlets (e.g., Moita), (5), Amphibolites (e.g., Pari), and (6), Disseminated to massive base-metal sulfides (e.g., Bico de Pedra). The first four types of deposits are epigentic (orogenic) gold deposits, similar to those found in greenstone belts worldwide. The last two are unusual types of gold deposit, peculiar to the Quadrilátero Ferrífero. Bico de Pedra is a polymetallic Au–Ag–Zn–Pb–Cu deposit related to an aplite intrusion, whereas Pari is a stratiform Au-bearing-banded iron formation metamorphosed to epidote–amphibolite metamorphic facies. [Copyright &y& Elsevier]

Abstract: The Morro Velho gold deposit, Quadrilátero Ferrífero region, Minas Gerais, Brazil, is hosted by rocks at the base of the Archean Rio das Velhas greenstone belt. The deposit occurs within a thick carbonaceous phyllite package, containing intercalations of felsic and intermediate volcaniclastic rocks and dolomites. Considering the temporal and spatial association of the deposit with the Rio das Velhas orogeny, and location in close proximity to a major NNW-trending fault zone, it can be classified as an orogenic gold deposit. Hydrothermal activity was characterized by intense enrichment in alteration zones of carbonates, sulfides, chlorite, white mica±biotite, albite and quartz, as described in other Archean lode-type gold ores. Two types of ore occur in the deposit: dark gray quartz veins and sulfide-rich gold orebodies. The sulfide-rich orebodies range from disseminated concentrations of sulfide minerals to massive sulfide bodies. The sulfide assemblage comprises (by volume), on average, 74% pyrrhotite, 17% arsenopyrite, 8% pyrite and 1% chalcopyrite. The orebodies have a long axis parallel to the local stretching lineation, with continuity down the plunge of fold axis for at least 4.8 km. The group of rocks hosting the Morro Velho gold mineralization is locally referred to as lapa seca. These were isoclinally folded and metamorphosed prior to gold mineralization. The lapa seca and the orebodies it hosts are distributed in five main tight folds related to F1 (the best examples are the X, Main and South orebodies, in level 25), which are disrupted by NE- to E-striking shear zones. Textural features indicate that the sulfide mineralization postdated regional peak metamorphism, and that the massive sulfide ore has subsequently been neither metamorphosed nor deformed. Lead isotope ratios indicate a model age of 2.82±0.05 Ga for both sulfide and gold mineralization. The lapa seca are interpreted as the results of a pre-gold alteration process and may be divided into carbonatic, micaceous and quartzose types. The carbonatic lapa seca is subdivided into gray and brown subtypes. Non-mineralized, gray carbonatic lapa seca forms the hanging wall to the orebodies, and is interpreted as the product of extreme CO2 metasomatism during hydrothermal alteration. This dolomitic lapa seca ranges in composition from relatively pure limestone and dolomite to silty limestone and dolomite. The brown carbonatic and micaceous lapa secas are the host rocks to gold. These units are interpreted to correspond to the sheared and hydrothermal products of metamorphosed volcaniclastic and/or volcanic rocks of varying composition from dacitic to andesitic, forming various types of schists and phyllites. The high-grade, massive sulfide orebodies occur at the base of the gray carbonatic lapa seca. Both disseminated mineralization and quartz veins are hosted by micaceous lapa seca. The data are consistent with a model of epigenetic mineralization for the lapa seca, from a hydrothermal fluid derived in part from the Archean basement or older crust material. [Copyright &y& Elsevier]

The Crixa´s greenstone belt, central Brazil, is a volcanosedimentary sequence comprised of ultramafic and mafic metavolcanic rocks at the base and detrital and chemical metasedimentary rocks at the top. The sequence is part of the Archean sialic block exposed in the central part of the Neoproterozoic Brası´lia belt and therefore is strongly affected by the Brasiliano orogeny. Important gold deposits, such as Mina III, are mainly associated with carbonaceous and Fe- and Al-rich metasedimentary rocks of the upper unit.Sm–Nd isochron data for the basal metakomatiites and metabasalts indicate an age of 3.00±0.07 Ga. However, Nd isotopes for the upper metasedimentary rocks show TDM model ages of mostly 2.33–2.49 Ga, which indicates that neither they nor the associated Au mineralization are Archean. Also, garnet whole-rock dating for a Au-bearing chlorite–garnet schist yields an age of 505±7 Ma, suggesting that the mineralization is Neoproterozoic. The Nd model ages suggest that the metasedimentary sequence of Crixa´s represents a thrust sheet of Proterozoic rocks emplaced over the Archean terrains during the Neoproterozoic Brasiliano orogeny. [Copyright &y& Elsevier]

• Provenance of the Crixás greenstone belt's metagraywackes and carbonaceous phyllites. • Integrated data indicate a proximal intraoceanic arc-related source area. • Detrital zircon geochronology shows a dominant peak at ca. 2.1 Ga. • Syn-orogenic sedimentation took place in a Rhyacian trench or forearc setting. The Crixás-Goiás Domain, Central Brazil, comprises an association of Archean TTG (tonalite-trondhjemite-granodiorite) and Archean-Paleoproterozoic greenstone belts. The Crixás greenstone belt, located in the northern part of the domain, is constituted of Mesoarchean metakomatiites and metabasalts overlaid by Paleoproterozoic carbonaceous phyllites and metagraywackes that host important gold deposits. In this work, we present new integrated petrographical, geochemical and isotopic data to investigate the provenance and tectonic setting of the metasedimentary rocks of the Crixás greenstone belt. Mineral and textural immaturities, particularly of the metagraywackes, are consistent with a proximal source area; which is also evidenced by the chemical aspects that denote absence of significant sediment sorting and recycling. Geochemical data indicate provenance from mixed mafic and felsic sources. U-Pb detrital zircon geochronology shows unimodal age spectra, with a dominant peak at ca. 2.2–2.1 Ga and minor contribution of ca. 2.7 and 2.4 Ga grains. Concordia diagrams yielded upper intercepts between 2213.4 ± 5.6 and 2162.2 ± 9.2 Ma, interpreted as the age range of the main source area. The rocks present relatively homogeneous Sm-Nd model ages (2.44 to 2.34 Ga) and slightly negative to positive ƐNd, ranging from −0.27 to +1.25. We argue that the original sedimentary protoliths were deposited in a trench or forearc basin related to a ca. 2.2–2.1 Ga island arc formed adjacent to an Archean paleocontinent constituted of TTG-greenstone terranes. Rapid erosion of the rising intraoceanic arc resulted in syn -orogenic sedimentation that started with deep ocean black shale deposition in an anoxic environment followed by episodic turbidite currents of poorly-sorted immature sands. Sedimentary rock layers were tectonically transported to the continent and preserved in the elongated keels of Mesoarchean mafic–ultramafic volcanic rocks. This orogeny can be correlated with the amalgamation of the Goiás Massif during the Siderian-Rhyacian crustal growth related to successive collage of arc-related terranes in the formation of the western margin of the São Francisco paleocontinent. Sediment provenance of the Crixás greenstone belt proved to be crucial to the recognition and characterization of Paleoproterozoic crust that are apparently no longer preserved in outcrops. [ABSTRACT FROM AUTHOR]

The Crixás Greenstone Belt, located in an Archean-Paleoproterozoic terrane within the Neoproterozoic Tocantins Province, hosts an important gold deposit in Brazil with an endowment of 7 Moz currently operated by AngloGold Ashanti. Its stratigraphy is composed of an Archean komatiite and basalt basal sequence followed by a Paleoproterozoic sedimentary sequence composed of carbonaceous phyllites, dolomite-rich marbles with minor siliciclastic lenses (Ribeirão das Antas Formation) followed by a uniform siliciclastic sequence (Córrego Geral Formation). At the mining area, the entire sequence is stratigraphically overturned and metamorphosed under greenschist to lower amphibolite facies conditions. The orebodies are structurally controlled by thin-skinned low-angle thrust faults, and are mainly hosted by the sedimentary sequence in dilation zones named locally, from the shallowest to the deepest, as Structure Palmeiras, Structure IV and Structure III. The gold mineralization occurs in association with disseminated sulfides, massive sulfide lenses or quartz veins. Structure III is the deepest mineralized structure with gold mostly occurring in quartz veins cutting carbonaceous phyllites. Siliciclastic lenses occurring within the Structure III interval show variable gold grades, while siliciclastic rocks from the uniform deeper sequence just below Structure III are barren. The chronology of the sedimentary deposition, metamorphism and mineralization is still poorly understood. Detailed drill core logging, petrography and U–Pb geochronology of detrital zircons from siliciclastic rocks were carried out in order to better understand the relationship between the two metasedimentary packages and gold distribution. Petrographically there are no relevant differences between Au-bearing siliciclastic rocks (Ribeirão das Antas Formation) and barren siliciclastic rocks (Córrego Geral Formation), except for the presence of sulfides in the former. The new dataset of detrital zircon U–Pb ages revealed a ubiquitous Paleoproterozoic peak in all samples, with nearly no Archean contribution. K-feldspar and lithic angular fragments, zircons with low to medium roundness, and the U–Pb results indicate a Rhyacian provenance from a proximal source. Neoproterozoic overgrowths are found on detrital zircons from the barren siliciclastic interval of the Córrego Geral Formation, providing unequivocal evidence of a Neoproterozoic event around 600 Ma that affected the rocks. The Neoproterozoic partial reset, possibly related to the overriding of the Mara Rosa Magmatic Arc onto the Crixás Greenstone Belt, is unlikely to be linked to the mineralization considering that zircons from the barren rocks are the most thermally affected by this event. The Au mineralization is more likely related to Paleoproterozoic events, a time period known as a major global episode of orogenic gold deposit formation. • New U–Pb DZ data from the Crixás Greenstone Belt gold deposit. • Comparison between the Au-bearing and barren siliciclastic rocks. • Ubiquitous unimodal Rhyacian provenance. • Neoproterozoic partial resetting stronger in DZ from barren rocks. • Mineralization possibly related to the Paleoproterozoic major global episode of orogenic gold [ABSTRACT FROM AUTHOR]

The Quadrilátero Ferrífero (QF) is an important, polydeformed mineral province, located in the southernmost portion of São Francisco Craton. The Rio das Velhas greenstone belt (RVGB) is an Archean meta-volcano-sedimentary succession from the QF, the Córrego do Sítio unit (CdS) being its most widely distributed sedimentary sequence. Detailed sedimentology study allied to x-ray diffraction-XRD and geochronological (LA-ICP-MS in detrital zircon) analyses provide evidence for a new interpretation of the CdS. The identified sedimentary structures of the CdS (e.g. flaser and lenticular bedding, sharp and erosional base, normal grading, mud drapes, quartz granules, syndepositional deformation, and ball & pillow) led the interpretation of these couplets as turbidity currents deposits corresponding to TA and TE facies of the classic Bouma Sequence. The CdS sequence was deposited on distal portions of an ancient submarine fan environment by turbidity current mechanisms, then it was partially reworked by tidal bottom currents. Geochronological data pointed out the main influence of the Rio das Velhas II magmatic event in the deposition of the eastern QF metasedimentary sequence, as evidenced by the maximum depositional age at 2818 ± 31 Ma. The surrounding metamorphic complexes terrains may have acted as source areas during the deposition of the sedimentary sequences, probably in a convergent to a collisional marginal tectonic setting (subduction stage). • Córrego do Sitio unit sedimentary sequences interpreted as turbiditity currents partially influenced by tidal bottom currents. • Eastern Rio das Velhas greenstone belt metagraywacke maximum depositional age at 2818 ± 31 Ma. • Sedimentary provenance from surrounding Archean metamorphic complexes. [ABSTRACT FROM AUTHOR]

• Characterization of recently discoveries s hear-zone-related gold mineralization. • Quartz-carbonate veins systems at Cuiabá world class gold deposit. • Vein classification, mineralogical and textural characteristics. • Vein structural analysis and hydrothermal fluid evolutionary model proposition. • Host rock hydrothermal description. • Using vein analysis in brownfields exploration context. The Cuiabá deposit, located in the Quadrilátero Ferríferro district (QF) in the southeastern part of the Minas Gerais state, is the largest underground mine in Brazil (5.78 Moz resources of 10.26 g/t Au − 1.18 Moz of ore reserves and 6 Moz of overall production). This world-class orogenic gold deposit is part of the Rio das Velhas greenstone belt, a typical association of mafic volcanic rocks, banded iron formation (BIF), carbonaceous and micaceous phyllites, metamorphosed to the greenschist facies conditions. Historically, economic gold production at Cuiabá derives from BIF-hosted, replacement-style sulfide (pyrite and pyrrhotite) ores. More recently, economically significant shear-zone-related gold mineralization in quartz-carbonate veins systems, hosted in metamafic rocks, were identified. They are associated with distal (chlorite-), intermediate (carbonate-) and proximal (sericite-dominant) hydrothermal alteration zones. Structures related to the gold-bearing quartz-carbonate veins were generated during a single, progressive ductile to brittle deformational event (D1), with the compositional banding S b and the flexural foliation S f created in the early stages of deformation. As deformation progressed, shear zones, isoclinal folds, the mylonitic foliation S m , the mineral lineation L min and the intersection lineation L int were formed simultaneously to the main stage of hydrothermal fluid input. Flanking folds and flanking shear bands represent the late stage of deformation and the final hydrothermal fluid pulse. Four quartz-carbonate vein systems are identified: V1, V2, V3 and V4. The V1 mineralized system is an S m -controlled fault-fill type, associated with the principal, gold-bearing fluid input stage. The V2 veins are also mineralized, controlled by the S f foliation and subdivided in three sub-types, according to internal crystal orientation: V2a extensional, V2b oblique-extensional and V2c, a fault-fill vein. The extensional array V3 veins are also controlled by the S m foliation, whereas the extensional, breccia-style V4 system has veins associated with flanking structures. The structural analysis of veins indicates a shortening vector rotation during D1 accompanied by hydrothermal fluid input. Since all vein systems are related to the D1 event, each one defining an incremental deformational stage, they provide information about the hydrothermal fluid evolution at Cuiabá. A proposed evolutionary model for the vein systems suggest that the ore-forming fluid responsible for gold mineralization was channeled along shear zones and dispersed out into the S b and S f structures. The internal vein features and the trapping temperatures of quartz from each vein system indicate a progressively decrease in tectonic activity. [ABSTRACT FROM AUTHOR]

The Quadrilátero Ferrífero region is located in the extreme southeast of the Brasiliano São Francisco craton, Minas Gerais state, Brazil. It is composed of (i) Archean TTG granite-gneaissic terranes; (ii) the Archean Rio das Velhas greenstone belt; (iii) the Proterozoic metasedimentary and metavolcano-sedimentary covers. The Rio das Velhas rocks were deposited in the synformal NW–SE-directed Nova Lima basin. The Archean deformation converted the Nova Lima basin into an ample synclinorium with an eastern inverted flank. Archean orogenic gold mineralization within the Rio das Velhas greenstone belt rocks is controlled by NNW–SSE-directed, Archean regional shear zones subparallel to the strata of the Nova Lima synclinorium borders. Transamazonian and Brasiliano orogenies are superposed onto the Archean structures that control gold mineralization. In the eastern domain, Brasiliano fold-and-fault belts prevail, whereas in the western domain Archean and Transamazonian structures abound. The present study focus mainly is the western domain where the Cuiabá, Morro Velho, Raposos, Lamego and Faria deposits are located. Gold orebodies plunge to the E–NE and are tectonically controlled by the Archean D1–D2 deformation. The D3 Transamazonian compression—Which had a SE–NW vector sub-parallel to the regional mineralized Archean foliation/bedding—Buckled these structures, resulting in commonly open, synformal and antiformal regional folds. These are well documented near the gold deposits, with NE–SW axial traces and fold axes plunging to E–NE. Such folds are normal to inverted, NW-verging, with an axial planar foliation dipping moderately to the SE. The Transamazonian compression has only been responsible for the reorientation of the mineralized Archean gold ores, due to coaxial refolding characterized by an opposite tectonic transport. It has therefore not caused any other significant changes. Thrust shear zones, sub-parallel to the strong Transamazonian foliation, have given rise to localized metric segmentation and to the dislocation of gold orebodies. Throughout the region, along the towns of Nova Lima to Sabará, structures pertaining to the Brasiliano Araçuaí orogeny are represented only by gentle folding and by a discrete, non-pervasive crenulation cleavage. Thrust-shear zones and small-scale normal faults have caused, at most, metric dislocations along N–S-oriented planes. [ABSTRACT FROM AUTHOR]

The Quebra Osso komatiite flow field is part of the 2.9–2.7 Ga Rio das Velhas greenstone belt, in the Quadrilátero Ferrífero province, located in the Southern São Francisco craton (Brazil). It is mostly composed of metamorphosed komatiites with a minor association of pyroclastic and metasedimentary rocks. Through a detailed and systematic study, the komatiite flows were subdivided into coherent facies (massive, layered, and pillowed facies) and autoclastic facies (autobreccias and hyaloclastites), formed by effusive flows; and minor pyroclastic facies (tuffs and lapilli-tuffs) that are related to explosive flows. The igneous textures are still preserved, although their primary minerals (olivine and pyroxene) were completely pseudomorphosed by serpentine and/or chlorite. The major proportion of the komatiites of Quebra Osso Group is massive and cumulate-textured, which suggests channelized flow systems. The layered flows are subordinate and encompass an upper zone of random spinifex that grades to a lower cumulate zone. They are restricted to the marginal zones and interpreted as breakouts of lava from the main pathway. The occurrence of pillow lavas, hyaloclastites, and chemical sediments suggests that lavas erupted in a submarine environment. The abundance of autobreccias and local hybrid rocks point out to turbulent percolation of komatiites and/or multiple influxes of melts that caused the fragmentation of the solidified lava and magma mixing/mingling. The studied komatiites were variably affected by hydration due to seafloor alteration, regional metamorphism, and hydrothermal alteration. The mineral assemblage is secondary and comprises serpentine (mostly antigorite), chlorite, tremolite, talc, carbonate, and opaque minerals as accessory phases. The chemical composition of chromites suggests metamorphic overprint up to lower amphibolite facies conditions. Some komatiites are enriched in LREE (La, Sm, Nd), Rb, Ba, Th, Zr, Ti, and Y, and exhibit low [Nb/Th] MN , suggesting contamination by continental crustal. The bulk-rock and the mineral chemistry of amphibole, serpentine/chlorite, and chromite show enrichment of Al and decrease in Si contents in the spinifex-textured komatiites, as a result of crustal material assimilation and/or hybridization processes. The partial melting model for the HREE composition refers to a 50% batch melting of a garnet-free source with a composition similar to the pyrolytic mantle. The formation of Quebra Osso komatiite lavas is associated with the ascension of a mantle plume that was subsequently erupted onto the Archean sialic crust of the Santa Bárbara Complex and was later reworked by subsequent metamorphic and deformational events. • First systematic description of the volcanic facies of the Quebra-Osso Group. • Volcanic flows include massive, layered, breccias and minor pyroclastic rocks. • A fissural komatiite flow field emplaced into the TTG Santa Bárbara Complex. • Crustal assimilation had an important influence on the generation of these rocks. • It refers to 50% batch melting of a garnet-free source similar to the pyrolytic mantle. [ABSTRACT FROM AUTHOR]

• Gold-related events in the Rio das Velhas Greenstone Belt were translated into mineral system components. • Inferences about geological processes that lead to the formation of Archean orogenic gold mineralization at multiple scales. • Footprints of gold districts delineated by way of spatial modeling. • Targeting insights gained from public-domain datasets. There has always been a need for new methodologies and research to improve the decision-making process at the early stages of mineral exploration. This article presents a novel approach to integrating geodata in support of a mineral systems-based spatial analysis of orogenic gold deposits in the Rio das Velhas Greenstone Belt (RVGB), Quadrilátero Ferrífero Province, Brazil. The gold mineralization in the RVGB is spatially associated with thrust faults and shear zones and mainly hosted by iron-rich rocks such as mafic–ultramafic sequences and banded iron formations. To best represent the targeting elements of this mineral system spatially, a knowledge-based fuzzy logic method was employed to map the expressions of the gold depositional processes at the province (1:500,000), district (1:100,000) and camp (1:50,000) scales. At each scale, multivariate statistical techniques served to enhance multiple geological, geophysical, and geochemical datasets and extract from these data spatial proxies of the gold depositional processes. The results of this multi-scale predictive analysis were as follows: The first, province-scale model (M1) identified the entire gold prospective tract and the areas within it that may be of greatest relevance to future exploration. The second, district-scale model (M2) identified the different gold camps within the prospective tract and mapped the areas of gold favorability in a more detailed manner. The third, camp-scale model (M3) identified areas that, based on the current knowledge and distribution of high resolution geodata, are the most favorable whilst also being small enough as to permit target testing using conventional mineral exploration tools such as geophysics, geochemistry and/or drilling. The results obtained from our predictive models were validated by comparing them against the known gold occurrences using ROC (receiver operating characteristics) curves and AUC (area under the curve) graphs. According to these validations, model M1 scored an accuracy of 93.38%, whereas models M2 and M3 scored accuracies of 88.31% and 93.38%, respectively. A key observation made in the course of this study is that the gold prospective area as predicted by models M1, M2 and M3 varies according to the scale of the analysis. A novel factor in our approach is that we aimed assess the targeting criteria and spatial datasets that underpin them according to their spatial resolution and presented the results in form of integrated maps. In addition, the tools developed in this study have the capacity to reduce the cost of direct detection technologies regarding the transition from broad regional to camp scale at the early stages of mineral exploration, where the most initial decisions in search and area reduction are critical. [ABSTRACT FROM AUTHOR]

• There is evidence for local redox transitions 300 Ma years prior to the GOE. • Multiple proxies suggest euxinia preceded the expansion of oxidizing conditions. • Sulfur isotopes indicate oxidative weathering added sulfate to the Pitangui basin. • Sulfate and oxygen availability increased up-section. Geochemical evidence for local redox transitions is observed 300 Ma years prior to the Great Oxygenation Event (GOE ca. 2400 Ma) and suggests evolving environmental conditions through a continuous sequence where euxinia (anoxic and sulfidic) preceded the expansion of more oxidizing conditions. Based on multiproxy data such as iron speciation (Fe Py /Fe HR > 0.7) and Mo enrichments (varying from 3 to 64), we present one of the oldest records of euxinia from the Archean Pitangui greenstone belt (~2700 Ma), Minas Gerais, Brazil. The sulfur isotopic composition of sedimentary sulfides indicates early inputs of sulfate from oxidative weathering and an attenuation of sulfur mass independent fractionation that combined with other geochemical signatures (Fe HR /Fe T, Ce anomalies and rare earth element fractionation) is consistent with the expansion of oxygen availability, and suggests localized oxic conditions before the GOE. [ABSTRACT FROM AUTHOR]

• 3.4–3.3 Ga TTGs were products of partial melting of E-MORB and minor crustal sources. • 3.1–2.7 Ga successive magma addition denotes the first continental arc in the GCB. • Archean crust was intensely reworked in episodic tectono-thermal events (2.7/2.1 Ga). • 2.0 Ga crust represents the collisional event and further cratonization of GCB. The north-central part of the São Francisco Craton (SFC) is one of the oldest terranes in the South American platform and experienced three regional magmatic events at 3.4–3.3, 3.1–2.7, and 2.1 Ga. Our new SHRIMP U-Pb data place the origin of Guanambi-Correntina block (GCB) in the Paleoarchean, contemporaneous with the Gavião block in central north SFC. Lithological, geochemical, and isotopic evidence indicate that the 3.4–3.3 Ga rocks of the Favelândia complex are derived from partial melting of E-MORB sources during flat subduction. The 3.1–2.7 Ga K-granitoids in the Santa Izabel complex are derived from a mixture of crustal and mafic sources, as evidenced by the slightly negative to positive Ɛ Nd(T) and Sr/Sr i between 0.700 and 0.706. The 3.1–2.7 Ga event is responsible for the recycling of the Paleoarchean TTG crust, generation of low- to high-K evolved crust, and juxtaposition of the Favelândia and Santa Izabel complexes. The youngest magmatic event at ca. 2.1 Ga produced felsic plutons, derived from anatexis of Archean felsic rocks and mantle components. The collisional process tectonically juxtaposed the Riacho de Santana greenstone belt and Archean felsic rocks at 2.1–2.0 Ga, determining the region's current configuration. Based on the data reported in this study and previously published data, we suggest that the Guanambi-Correntina block was formed as an independent unit in the northern SFC. [ABSTRACT FROM AUTHOR]

• Contrasting styles of gold mineralization developed during the same deformation event. • Temperature ranges of ca. 330–410 °C are estimated for the gold mineralization event. • Gold mineralization is similar to other orogenic gold systems in Brazil and worldwide. The Faina greenstone belt is located in central Brazil and contains the Cascavel and Sertão gold deposits (500,000 oz Au total resource and past production). The bulk of the gold is hosted in quartzite and biotite schist at Cascavel, and carbonaceous schist and banded iron formation at Sertão. The metamorphic grade of the host rocks is greenschist facies. Cascavel is a vein-hosted gold deposit with orebodies mainly controlled by F 2 fold hinges, with minor mineralization in D 3 shear zones. Hydrothermal alteration in quartzite is characterized by distal quartz-K-feldspar ± muscovite, intermediate quartz-fuchsitic mica-biotite-pyrite, and proximal quartz-white mica-pyrite ± chalcopyrite. The biotite schist is characterized by distal quartz-chlorite-calcite and proximal white mica-biotite-tourmaline-siderite-pyrite. Native gold is located within intensely deformed quartz veins, and locally as free gold disseminated in proximal alteration zones. Sertão is a shear zone-hosted gold deposit with orebodies controlled by D 3 shear zones including gold-bearing shear veins and surrounding hydrothermally altered wallrocks. Hydrothermal alteration is characterized by distal quartz-ankerite-chlorite-pyrite ± chalcopyrite and proximal quartz-white mica-siderite-pyrite-arsenopyrite ± chalcopyrite. Gold is in equilibrium with arsenopyrite and within arsenopyrite disseminated in the proximal alteration zone. Chlorite geothermometry suggests temperatures of 335–407 °C and 328–397 °C for the gold-bearing hydrothermal fluids in the Sertão and Cascavel deposits, respectively. Arsenopyrite geothermometry on arsenopyrite within gold-bearing veins in the Sertão deposit yields temperatures between 310 and 480°C. Structures controlling hydrothermal alteration and gold mineralization in both deposits are developed during a regional D 2 event and subsequently deformed during a D 3 event. Hydrothermal alteration minerals are consistently replacing metamorphic minerals. The alteration assemblages in both deposits are similar, albeit their modal mineralogy is controlled by the host rock composition. Therefore, both the Cascavel and Sertão deposits are interpreted as orogenic, mesozonal gold systems comparable with other orogenic gold systems in Brazil and worldwide. [ABSTRACT FROM AUTHOR]

The Pitangui greenstone belt (PGB) – located in the southern São Francisco Craton, (Brazil) – is a volcano-sedimentary assemblage that is tectonically imbricated over the orthogneiss and granitoid rocks collectively termed the Divinópolis Complex. One diorite gneiss sample from the northern Divinópolis Complex yields an igneous zircon age of 2878 ± 5.7 Ma, constraining the time of crystallization. The basal sequence of PGB predominantly comprise metabasalt with restricted bodies of metagabbro/metadiorite, metaultramafic volcanic rocks and BIF. The upper sequences of the PGB exhibit a maturation of the basin, grading to more felsic and sedimentary lithologies, such as clastic metasedimentary rocks, intermediate metavolcanic rocks, and metapyroclastic rocks. The first recognized deformation phase in the PGB (D n) is associated with greenschist facies conditions and the development of the main tectonic foliation. The second deformation phase (D n+1) is associated with amphibolite facies metamorphism, while a later (D n+2) phase may be related to younger Proterozoic deformation (ca. 2.0 Ga). PGB metabasalts yield a crystallization age of 2740.2 ± 12 Ma and are characterized by a tholeiitic affinity and flat LREE patterns. Based on mixed MORB- and arc-affinities, a back-arc basin setting is suggested for the formation of PGB basalt. This mafic magmatism (2740 Ma) is slightly younger than the ages reported for the Rio das Velhas greenstone belt, with which the PGB is generally correlated. The metasedimentary rocks of the PGB have age intervals spanning from 2690 to 3250 Ma. One mica-quartz phyllite has a maximum depositional age of 2769.8 ± 8.9 Ma while a chlorite phyllite records and age of 2693.2 ± 7.9 Ma. The metasedimentary rocks are derived from a source area of mafic to felsic composition that is similar to TTGs, cratonic Archean shales and E-MORB. The predominant sources were likely the sialic Archean crust of the granite-gneiss complexes (e.g. the Divinópolis Complex and potassic granitoids of the Mamona Event) and the mafic sequences of the arc (e.g. PGB back-arc basalt). One late potassic pluton (Casquilho monzogranite) crosscutting the fabrics of the volcano-sedimentary assemblage and yields an intrusion age of 2694.7 ± 9 Ma, constraining the minimum sedimentation age assembly of the package. Collectively, a Neoarchean primitive island arc or back-arc basin is proposed to have generated the PGB, which is here interpreted as distinct from the Rio das Velhas greenstone belt. We suggest that PGB developed during an accretion-collision event in the southern São Francisco Craton before cratonic stabilization of the crust by the end of the potassic 2760-2680 Ma Mamona Event. • Crystallization age of the Divinópolis Complex diorite gneiss is 2878 Ma. • Mafic magmatism of Pitangui greenstone belt at 2740 Ma. • Metasedimentary rocks originated from sources between 2690 and 3350 Ma of felsic and mafic composition. • The minimum depositional age of sediments is constrained by the intrusion of the Casquilho granite at 2694 Ma. • Pitangui greenstone belt is younger than Rio das Velhas greenstone belt. [ABSTRACT FROM AUTHOR]

Metamorphosed mafic-ultramafic rocks from the central portion of the Rio Grande do Norte Domain of the Borborema Province (BP), northeastern Brazil, have been studied here with the objective of gaining a better understanding of the Archean evolution of this portion of the BP. The study area is underlain by gneissic-migmatitic basement as well as biotite schists and paragneisses of the Seridó and Jucurutu formations of the Seridó Group. The mafic-ultramafic rocks (serpentinites, amphibole-schists and amphibolites) occur in lenses for 30 km along strike following the NNE regional foliation. The serpentinites occur as relatively small exposures of elongated bodies within paragneisses of the Jucurutu Formation and orthogneisses of the Caicó Complex. They consist of xenoblastic serpentine (75–99%) that has replaced the primary ferromagnesian minerals of the protolith. The amphibole schists and amphibolites are whitish gray to green, depending on the dominant mineral phase, tremolite, talc or actinolite. The mafic-ultramafic rocks present high MgO, Ni and Cr 2 O 3 contents and very low TiO 2 , Na 2 O and K 2 O contents, being compositionally similar to mafic-ultramafic rocks from other Archean greenstone belts worldwide. U-Pb (SHRIMP) dating of zircons returned concordia ages of 3526 ± 5 Ma (MSWD = 0.0084) for the serpentinites of the Serra Verde Mine and 3747 ± 12 Ma (MSWD = 9.8) for serpentinites from the Oiticica Mine. The petrographic and geochemical characteristics as well as the Eo to Paleoarchean ages of the studied rocks are significant as the basement of this portion of the BP is dominantly of Paleoproterozoic age. It is envisaged that these results will lead to further debate and a greater understanding of crustal evolution of the BP. We propose that these mafic-ultramafic rocks are part of a dismembered Archean greenstone belt, which present the oldest ages so far determined for the South American Platform. • The mafic-ultramafic rocks have geochemical signatures akin to Archean komatiites. • The mafic-ultramafic rocks may be a part of a dismembered greenstone belt. • Zircon U-Pb dating indicates Eo to Paleoarchean crystallization ages for the protoliths. • Archean crust in this part of Borborema Province may be more extensive than previously thought. [ABSTRACT FROM AUTHOR]

The Crixás Greenstone Belt is a supracrustal rock sequence of the allochthonous Archean-Paleoproterozoic Crixás-Goiás Terrane of the Neoproterozoic Tocantins Province of Central Brazil. The belt occurs between Mesoarchean (2.9-2.8 Ga) primitive orthogneiss complexes intruded by Siderian intracratonic mafic dikes and stocks. The rock succession of the greenstone belt consists of metakomatiites followed by metabasalts, both of greenschist to low amphibolite facies, underlying metasedimentary rocks of low greenschist facies. The greenstone belt is divided into the southern, central, and northwestern sectors, with different rock associations. The northwestern sector tectonically underlies a small exotic block known as the Mina Inglesa Sequence. The sequence consists of a low greenschist facies volcano-sedimentary package similar to a greenstone belt, but of unknown origin. The latest stratigraphic nomenclature for the belt labels its rock package as the Crixás Group. From base to top, the Group comprises the Córrego Alagadinho, Rio Vermelho, and Ribeirão das Antas Formations, made up of metakomatiites, metabasalts, and metasedimentary rock, respectively. The Mina Inglesa Sequence is an independent unit of the Crixás Group, in spite of the similar rock assemblage of both units. Protoliths of the Ribeirão das Antas Formation comprise shallow water black shales with dolomite lenses, laterally wedge-shaped with impure turbiditic sandstones (wakes). Published U/Pb and Sm/Nd whole-rock isotopic data indicate that the metakomatiites and metabasalts erupted during the Mesoarchean (3.0 Ga). Detrital zircon grains from the sedimentary protoliths suggest a mixed Mesoarchean and Rhyacian source-area (3.2 and 2.2 Ga). The U/Pb age from hydrothermal zircon grains of a gold-bearing quartz vein indicates that the sedimentation ended just before 2.1 Ga. Field, drilling, and the isotopic data led the authors to review the stratigraphic content of the Crixás Group by subdividing it into an Upper and Lower Subgroups. The Lower Subgroup comprises the Mesoarchean volcanic section subdivided, from base to top, into the currently adopted Córrego Alagadinho and Rio Vermelho Formations. The Upper Subgroup rests ubnconformable on the Lower Subgroup, and comprisess the Rhyacian metasedimentary section. The Upper Subgroup contains two rock units deposited in different environments. The currently used Ribeirão das Antas Formation is the lower unit, which is redefined as composed of carbonaceous phyllites with dolomite lenses. The upper unit comprises the new proposed Córrego Geral Formation, composed of metagraywackes. The wedge-shaped contact between both sedimentary units indicates that they were coevally deposited. The Paleoproterozoic sedimentary basin consisted of a small depression formed during the sagduction of the volcanic pile, triggered by the diapiric rise of the adjacent orthogneiss protoliths. The sediment deposition started with black shales in response to a slow rise of the seawater and paleoclimatic conditions. An increasing input of siliciclastic turbidites occurred in response to the uplift of a Rhyacian/Mesoarchean source-area that provided a mixed clastic load. Anomalous positive δ13C data from the dolomite lenses indicate that they deposited during the 2.2-2.1 Ga Lomagundi Event, which is compatible with the dominant Rhyacian zircon grains of the graywackes. The Crixás-Goiás Terrane lacks geologic evidence for the existence of an internal Rhyacian crustal block to justify the youngest detrital zircon grains of the graywackes. These observations render uncertainty about the geographic position of the rising crust. Paleoproterozoic crustal shortening of the belt resulted in stacked thin-skinned thrust-faults that host gold orebodies. An eastward age decrease of the crustal shortening from Crixás to an easterly belt leads the authors to propose that the clastic load source could occur to the West of the Terrane. The Mina Inglesa Sequence is an allochthonous block with lithologic and isotopic features that distinguish it from the greenstone belt. The authors also describe that there is no isotopic evidence for Meso- to Neoproterozoic source-areas, neither for the Córrego Geral Formation nor for the Mina Inglesa Sequence. These findings raise a suggestion that the granite-greenstone belt association of the Terrane may represent a craton border that remained stable before its amalgamation to the province during the Neoproterozoic. • Stratigraphic update of the Crixás Greenstone Belt, Central Brazil. • Subdivision of the Crixás Group into a Lower Sub-group of volcanic rocks, and an Upper Sub-group of metasedimentary rocks. • Subdivision of the metasedimentary section into two coeval formations. • U-Pb data from detrital zircon grains and discussion about source-areas. • Discussion about tectonic and depositional environments of the greenstone belt. [ABSTRACT FROM AUTHOR]

Minor altered intrusions and drab retrogressed schists can easily be overlooked in geological studies but this contribution explores these rocks within the Archaean and Palaeoproterozoic southern São Francisco Craton (SSFC), Brazil using geological relationships and accessory mineral in situ analyses in the context of cratonic assembly. Three magmatic pulses are documented: i) Archaean and ii) Palaeoproterozoic felsic intrusions, both hosted by Archaean protoliths, and iii) Palaeoproterozoic felsic intrusions in Palaeoproterozoic supracrustal sequences. Archaean felsic intrusions confirm the Palaeoarchaean age of the mafic/ultramafic sequence of the Rio das Velhas Greenstone Belt and Rhyacian intrusions mark the collisional stage of the Mineiro Belt with the SFC at c. 2130 Ma. Greenstone belt schists show a wide distribution of rounded 'soccer ball' Archaean detrital and metamorphic zircon grains ranging in age from 3200 to 2750 Ma with an interpreted overprinting high-grade metamorphic event at c. 2700 to 2680 Ma. Most high-grade metamorphic rims have Th/U > 0.1, negative εHf (t) values and REE pattern consistent with eclogite/granulite metamorphic facies, reinforcing the hypothesis of a dehydrated-refractory crust formed during the stabilization of the SSFC, even though no such protoliths are preserved. This event links crustal thickening and partial melting of Archaean lower crust. Archaean rutile crystals from the greenstone belt schist were reset during the Palaeoproterozoic event but still preserve the early Archaean high-grade metamorphic signature. The presence of unstable ilmenite replaced by rutile in the schist, associated to felsic intrusions with the same age at c. 2130 Ma suggest high pressure, low temperature prograde metamorphism during the collisional stage of the Palaeoproterozoic orogen. Elongate and prismatic zircon grains from the Rhyacian intrusions have low εHf (t) signature and crystallised from partial melting of sedimentary protoliths. Accretionary events produced thicker and more differentiated crust by the end of Rhyacian time. Easily overlooked rocks in this study, when studied, have revealed a rich multi-event history of cratonic evolution. • Archaean felsic intrusions constrain the Rio das Velhas Greenstone Belt evolution in at least 200 Myr; • High-grade soccer ball metamorphic zircon grains depict conditions of Archaean crustal amalgamation; • First report of Rhyacian felsic intrusions in the Minas and Rio das Velhas supergroups of the Quadrilátero Ferrífero; • Rhyacian felsic intrusions in the supracrustal sequences derive from reworked crust; • Rhyacian felsic magmatism around the margins of the SSFC depicts the collisional stage of the Minas accretionary orogeny. [ABSTRACT FROM AUTHOR]

Field, petrographic, lithogeochemical, LA-ICP-MS in situ U-Pb zircon geochronology, and Nd and Sr isotopic data were used to determine the geologic evolution, timing of volcanism and tectonic setting of the Mundo Novo greenstone belt (MNGB) including nearby units, such as the basement and younger granitic rocks in the eastern São Francisco Craton (NE Brazil). The basement of the greenstone belt corresponds to the Gavião Block, which comprises tonalite-trondhjemite-granodiorite orthogneisses, migmatites and subordinate metarhyolites and metagranites. The MNGB is divided into three lithological sequences: (i) the lowermost unit is composed of metakomatiites; (ii) the middle unit is composed mainly of metabasalts, metadacites and metasedimentary chemical rocks; and (iii) the uppermost unit is composed of metasedimentary siliciclastic rocks. Additionally, two Rhyacian-Orosirian granitic plutons occur in the area, the Areia Branca and Jequitibá metagranites. U-Pb zircon data from the Miguel Calmon and Fazenda Coqueiro metagranites in the Gavião Block yield crystallization ages of 3355 ± 16 Ma and 3227 ± 23 Ma, respectively, and both metagranites were derived from the lower continental crust based on low 87Sr/86Sr i values (0.699 and 0.705, respectively) and negative values of Ɛ Nd(t) (−3.7 and −3.6, respectively). The 2595 ± 21 Ma U-Pb zircon crystallization age of the metadacites allowed the determination of the timing of volcanism in the middle sequence of the MNGB. The 2106 ± 71 Ma and 1975 ± 36 Ma U-Pb zircon crystallization ages for the Areia Branca and Jequitibá metagranites, respectively, which are both interpreted as derived from crustal protoliths based on high 87Sr/86Sr i values (0.744 and 0.730, respectively) and negative values of Ɛ Nd(t) (−7.7 and −6.5, respectively), record a Rhyacian-Orosirian tectonothermal event that affected the MNGB and the adjoining region. The whole-rock geochemical data in tectonic discrimination and multielement diagrams show that the volcanic rocks of the MNGB formed in island arc and back-arc basin settings related to the oceanic crust. Therefore, the following five stages are proposed for the tectonic evolution of the study region: stages (i) and (ii) were characterized by the establishment of the TTG basement by 3.35 Ga, when the Miguel Calmon granite was consolidated, followed by a rifting that formed the rhyolites, and subsequent granite formations occurred at 3.22 Ga (Fazenda Coqueiro granite formation), followed by the abort of the rift and a closure event. The volcanism during stage (iii) at 2.59 Ga in the MNGB occurred in island arc and back-arc basins in the oceanic crust between Archean cratonic blocks, and stages (iv) and (v) between 2.10 Ga and 1.97 Ga represent two stages of a progressive collision event in which the oceanic crust was compressed between the Gavião, Mairi, Jequié and Serrinha blocks and the Itabuna-Salvador-Curaçá Belt from the eastern part of the São Francisco Craton. The collisional event of stages (iv) and (v) was coeval with the Rhyacian-Orosirian formation of granites and basins such as that where the uppermost siliciclastic sequence of the MNGB was deposited. • The Paleoarchean metagranites were derived from the lower continental crust. • The Mundo Novo greenstone belt formed in island arc and back-arc basin settings. • The volcanism in the Mundo Novo greenstone belt occurred at 2595 ± 21 Ma. • The Rhyacian-Orosirian granitic bodies were derived from crustal protoliths. • The oceanic crust was compressed between cratonic blocks during the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

The Serra das Pipocas Greenstone Belt is one of the rare Paleoproterozoic greenstone belts within the Borborema Province. It is on the west border of the Archean/Paleoproterozoic Nucleus (Cruzeta and Mombaça Complex) of the Ceará Central Domain, northern portion of the Borborema Province. The Serra das Pipocas Greenstone Belt has an elongated sigmoidal shape encompassing about 1000 km2 of the Ceará Central Domain. It consists of a metavolcanosedimentary sequence formed by metasedimentary psammitic-pelitic-marly rocks and interleaved metaultramafic and metamafic rocks, represented by chlorite-anthophyllite-actinolite/tremolite schists and amphibolites. Layers of metatuffs, metabasic, meta-acid sills (metadacites), metacherts, gondites and banded iron formations occur within the metamafic rocks. Actinolite, metagabbro, metadiorite bodies, metabasic dike, Neoproterozoic metagranodiorites and leucogranites crosscut the metavolcanosedimentary sequence. Close to the borders of metagranodioritic bodies (zircon U–Pb 2181 ± 4.4 Ma), the metavolcanosedimentary sequence is hydrothermally altered. The metaultramafic rock (chlorite-anthophyllite-actinolite/tremolite schist) contains high MgO (>18 wt%), low alkali (≤1 wt%) and TiO 2 (<0.8 wt%) and Al 2 O 3 /TiO 2 ratios between 9.94 and 27.26, with a mean value of 17.13. Values of (Gd/Yb) N vary between 1.00 and 1.88, which attest affiliation with komatiite protoliths, between the Munro and Barberton types. The amphibolites are usually fine-grained and depleted in ΣREE (33.14–45.02 ppm), with low (La/Yb) CH values (0.74–3.82). This reflects weak LREE enrichment in relation to HREE, and no Ce and Eu anomalies [(Eu/Eu*) n between 0.98 and 1.04]. Such patterns are similar to T-MORB (1.7–4.3). Additionally, some mafic-ultramafic metaplutonic rocks present chemical composition similar to their volcanic counterparts, and this may indicate cumulates or sills contemporary to this sequence. Zircon U–Pb dating using LA-ICP-MS of three distinct metadacite occurrences (western border: 2234 ± 13 Ma, eastern border: 2212 ± 13 Ma, and central portion: 2156 ± 45 Ma) and metagranodiorites (2181 ± 4.4 Ma) indicates that the sequence was formed during the Rhyacian/Orosirian and later affected by late Neoproterozoic. [ABSTRACT FROM AUTHOR]