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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]

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]

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 mineral system concept, which combines integrated information from all kinds of geological and geophysical studies, is a very useful approach to predict and locate structures and lithologies potentially associated with gold mineralization at all scales (i.e., upscaling from craton-to district-to camp-to deposit-scale). This is demonstrated in this study where the Yaou deposit, located in French Guiana within Rhyacian terranes, formed and deformed during the Trans-Amazonian orogenic cycle (ca. 2600-1950 Ma), is used as a case study. The deposit comprises numerous intrusions hosting the bulk of the high-grade gold mineralization at Yaou, associated with a quartz-carbonate veining system. Both intrusive and gold events are dated in order to constrain Yaou in the regional litho-structural framework. Spatially associated with the Central Yaou Shear Zone (CYSZ), one of the quartz monzodiorite yields a U–Pb zircon age of 2131 ± 6 Ma, supra-chondritic εHf t of ca. 2.5, and Hf model ages at ca. 2.6–2.4 Ga. These data suggest Paleoproterozoic rock formation due to reworking of juvenile crust, derived from the depleted mantle during the late Archean to early Paleoproterozoic. The main and economic gold event hosted by the quartz monzodiorite is dated at 2105 ± 25 Ma by Re–Os isotope analyses of Au-bearing pyrite, representing the first date for gold mineralization in French Guiana. A multi-scale approach using airborne magnetic and radiometric data allows to better understand the spatial distribution of the intrusions and possibly associated shear zones, both related to gold mineralization events. The intrusions and associated shear zones are interpreted as being parallel along a N60° trend and replicated laterally toward the northwest. A temporal association is defined between the shearing deformation and the magmatic event, both being synchronous with a possibility of pre-shearing intrusion and a protracted magmatic phase active while shearing. The Yaou-type intrusion-hosted mineralization can be targeted along these N60°-striking structures. This integrated approach opens some targeting options, previously unrecognized within the southern Paramaca Greenstone Belt. • A coupled geological-geophysical approach is proposed. • The Yaou gold deposit (French Guiana) is used as a case study. • Intrusions hosting the bulk of the gold mineralization, dated at 2131 ± 6 Ma (U–Pb on zircon). • The main and economic gold event is dated at 2105 ± 25 Ma (Re–Os on Au-bearing pyrite). [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]