The sediment-hosted stratiform copper-cobalt deposits in the Central African Copperbelt (CACB) are renowned for their resource potential, encompassing Cu-Co (Ni, U) and Cu-Zn-Pb (Ag, Ge, Mo, Cd) mineralization. Microstructural and microthermometric analyses of carbonate-quartz veins from the Tenke Fungurume mining district, situated in the central part of the Katanga Copperbelt (KCB), have delineated a pre- to post-folding paragenesis of vein formation and hypogene Cu-Co ore mineralization. The mineralization primarily consists of chalcopyrite, chalcocite, carrollite, and bornite. Pre-folding veins comprise bedding-normal veins related to the extension stage, occasionally linked with mullion development during the following compressional stage, as well as bedding-parallel beef veins. Synfolding mineralization manifests as saddle reef veins within fold hinge zones, fracture-filling veins aligned with tangential longitudinal strain in hinge zones of folded bedding-parallel veins, thin veinlets forming parallel to an axial-planar and shear-band cleavage, and bedding-parallel shear veinlets with oblique fiber orientations. The post-folding Cu-Co mineralization consists of veins that cross-cut earlier veins and folds. Microthermometric analysis of fluid inclusion assemblages from the pre-, syn-, as well as post-folding veins reveals the presence of different fluid types. A high-temperature (180-340 degrees C) and high-salinity (27-52.5 wt% NaCl + (KCl) eq.) fluid was responsible for the Cu-Co mineralization during the pre- to syn-folding stages. A hypersaline fluid (27.0-42.1 wt% NaCl eq.) with a broad range in temperature (45-387 degrees C) circulated during the post-folding stage of the Lufilian orogeny. A fluid exhibiting low to moderate homogenization temperatures (28-215 degrees C) and low to moderate salinity (3.4-23.0 wt% NaCl eq.) is related to fluid circulation during the postLufilian epoch. The wide range and variations in salinity of these three fluid types associated with Cu-Co mineralization provide evidence for a multistage fluid flow and a complex hydrothermal system linked to the deposition of Cu-Co ores within the Tenke Fungurume Mining District and the broader Katanga basin. This hydrothermal system has operated during diagenesis, the basin development stage to the Lufilian orogeny and the subsequent post-Lufilian period.

This paper presents the geometric analysis of sigmoidal en echelon vein system that formed by non-coaxial deformation within conjugate Riedel-shear zones. Both sinistral S-type and dextral Z-type vein arrays, which have a subparallel enveloping surface, are observed. Individual asymmetric quartz veins consist of (1) a central, thin slickenfibre shear vein that is separating (2) pennant-shaped extensional vein tips characterised by strong dilation. Our observations closely resemble the results from published analogue experiments, which suggest that dilation occurs along R and R′ Riedel shear fractures during progressive rotation and slip within brittle-ductile shear zones. The shear vein formed by incremental pull-apart in the extensional step of overlapping R′ shear fractures, as marked by the presence of solid inclusion trails and bands. The pennant veins opened in the obtuse angle between intersecting R’ and R shears. The close association with a kinked pre-existing tectonic foliation, which acted as a passive marker of non-coaxial deformation, allows a kinematic restoration of the initial conjugate shear zone geometry that formed under approximate NE-SW compression. This model could warrant the reassessment of the classic interpretation of sigmoidal en echelon vein systems that are associated with kink bands.

Many studies have constrained that late-Variscan buckling produced the arcuate geometry of the Ibero-Armorican belt. Nonetheless, debate remains on the associated geodynamic framework. Poorly studied Late Carboniferous intramontane basins offer an excellent framework to decipher the timing and kinematics of the late- to post-Variscan tectonics. Understanding the latter also helps constrain the structural emplacement mode of contemporaneous W–Sn–Nb–Ta–Li mineralization. In Iberia, the Porto–Sátão syncline is an example of such a Late Carboniferous intramontane basin. We present a structural analysis of the syncline, its basement and the associated W–Sn deposits. The regional structure is dictated by the Alcudian angular unconformity, caused by Cadomian tectonics (575–555 Ma) and separating tilted Ediacaran and subhorizontal Lower Paleozoic formations. Superimposed Variscan deformation led to F 1 –F 3 folds with steep and gentle plunges, respectively. The late-orogenic D 3 fabric is locally affected by post-orogenic F 4 kink folds and an S 4 crenulation cleavage. W–Sn-bearing vein systems occur along granite-hosted cone sheets, or exploit cross-fold joints associated with the F 3 and F 4 fold generations, revealing a close kinematic relationship between granite-related mineralization and the late- to post-Variscan deformation style. This structural history is interpreted as a plate-scale geodynamic change from Late Carboniferous north–south (D 3 ) to Early Permian WNW–ESE (D 4 ) convergence.

The geodynamic evolution of the Mesoprotemzoic Karagwe-Ankole Belt, situated in Central Africa, is largely unconstrained and topic of discussion. To overcome this knowledge gap, the tectonic history of the Western Domain has been studied, focusing on bedding, tectonic foliations and lineations, and quartz vein generations from the Kibuye-Gitarama-Gatumba area (West Rwanda). The results of our study reveal two fold generations, that are interpreted as the consequence of two separate compressional deformation events. The first fold generation (F-1) consists of regional-scale symmetrical folds, with a N30W to NS axial plane strike and variable foldcylindricity. The second generation (F-2) is expressed by local small-scale folds with a generally steep axial plane, superposed on the regional fold structure. The strike of the F-2 axial planes varies over the study area (N60W vs N20W), possibly linked to a buttressing effect from the rigid Gitarama batholith. Three quartz vein categories were determined: early quartz veins, strongly shortened or emplaced during F-1 (A-category), bedding-parallel, boudinaged quartz veins, deformed pre- to syn-F-2 (B-category) and undeformed, syn- to post-F-2 quartz veins (C-category). Based on geochronological data from literature, the first major compressional event can be connected to the Late Mesoproterozoic Rodinia assembly during the Stenian-Tonian, while the youngest tectonometamorphic event may represent the influence of the Late Neoproterozoic Gondwana assembly in the study area. This study furthermore demonstrates that the tectonic history of the Western Domain differs significantly from that of the Eastern Domain.

The W-Sn Panasqueira deposit consists of an extensive swarm of coplanar, subhorizontal veins that are laterally overlapping and connecting. Segmentation structures, a local zigzag geometry and straight propagation paths indicate that the veins are exploiting regional cross-fold joints. These joints are associated with subvertically-plunging F-3 folds, which developed during late-orogenic oroclinal buckling. Veining reactivated the joints under hydraulic overpressures and low differential stress. The consistent orthogonal relationship between the veins and non-cylindrical F-3 fold hinges indicates that veining occurred in a similar stress regime as jointing, i.e. with the minimum principal stress subparallel to the fold hinges. In-situ Rb-Sr dating (LA-ICP-MS/MS) of muscovite selvages bordering the vein walls has demonstrated that W-Sn mineralization occurred in a time range of 305-302 (+/- 2.3 to 4.1) Ma. Hence, the structural emplacement of the vein swarm occurred in a late-orogenic setting, simultaneous with transpressional F-3 folding and prior to the tectonic inversion at ca.297-295 Ma. Iberian vein-type W-Sn mineralization and oroclinal buckling thus appear not only to share their late-Variscan timing, but could also be considered as kinematically related processes.

The Cantabrian orocline is a major orocline that bends the Variscan belt of Western Europe. Despite a wealth of studies, its timing and relationship with the late-Variscan folding stages in the Iberian Massif are still debated. This study provides an integrated structural analysis of the Variscan fold generations and associated W-Sn bearing vein systems within the southern Central Iberian Zone (Regoufe, Portugal), giving insight into their kinematic relationship with oroclinal buckling. Two superimposed fold generations with mutually parallel, steep to vertical fold axes have been identified. Isoclinal F-1 folds with E-W striking axial planes formed during coaxial shortening and are spatially localised. F-3 folds with NW-SE axial planes are associated with late-Variscan transpressional deformation and constrain the structural outline of the major folds. Temporal and kinematic considerations indicate that vertical-axis, asymmetric F-3 folding corresponds with the expected deformation style within the southern limb of the Cantabrian orocline. The Regoufe area is characterised by two types of W-Sn vein-type mineralisation. Granite-hosted hydrothermal quartz veins show a concentric distribution and are associated with the stress regime during granite emplacement. The vein system within the metasedimentary host rock, however, is emplaced along a regional, subhorizontal cross-fold joint system. This cross-fold joint system developed orthogonal to the subvertical F-3 fold axes, and is interpreted to be coeval with oroclinal buckling. These results impact the understanding of (i) the relative significance and geometry of the main deformation stages in the Iberian massif, reconciling the timing and kinematics of F-3 regional folding with oroclinal buckling, and (ii) the kinematic relationship between late- to postorogenic deformation and W-Sn vein-type mineralisation.

The world-class W-Sn Panasqueira deposit consists of an extensive, subhorizontal vein swarm, peripheral to a late-orogenic greisen cupola. The vein swarm consists of hundreds of co-planar quartz veins that are overlapping and connected laterally over large distances. Various segmentation structures, a local zigzag geometry, and the occurrence of straight propagation paths indicate that they exploited a regional joint system. A detailed orientation analysis of the systematic joints reveals a geometrical relationship with the subvertical F 2 fold generation, reflecting late-Variscan transpression. The joints are consistently orthogonal to the steeply plunging S 0 –S 2 intersection lineation, both on the regional and the outcrop scale, and are thus defined as cross-fold or ac-joints. The joint system developed during the waning stages of the Variscan orogeny, when already uplifted to an upper-crustal level. Veining reactivated these cross-fold joints under the conditions of hydraulic overpressures and low differential stress. The consistent subperpendicular orientation of the veins relative to the non-cylindrical F 2 hinge lines, also when having an inclined attitude, demonstrates that veining did not occur during far-field horizontal compression. Vein orientation is determined by local stress states variable on a meter-scale but with the minimum principal stress consistently subparallel to fold hinge lines. The conspicuous subhorizontal attitude of the Panasqueira vein swarm is thus dictated by the geometry of late-orogenic folds, which developed synchronous with oroclinal buckling of the Ibero-Armorican arc.

The Nb-Ta-Sn pegmatites and Sn quartz veins of the Rwamagana-Musha-Ntunga area in eastern Rwanda are part of the Mesoproterozoic Karagwe-Ankole Belt. These commodities are on a regional scale spatiotemporally associated to the early Neoproterozoic fertile G4-granite generation. Although a transition from the lithium-cesium-tantalum pegmatites to cassiterite microcline quartz veins has been observed in the Rwamagana-Musha-Ntunga area, the structural control and the paragenetic relationship between the mineralized pegmatites and the Sn bearing quartz veins is largely unknown. Consequently, this study investigates the occurrence of pegmatites and quartz veins and the structural and lithological controls on their emplacement. The metasediments in the area are affected by a regional compressional regime with a shortening direction oriented N70E, which resulted in a N20W-oriented fold sequence. The Lake Muhazi granite is present in center of the Karehe anticline. The structural orientations of pegmatites and quartz veins show that two important factors control their emplacement. The first control is the reactivation of pre-existing discontinuities such as the bedding, bedding-parallel joints or strike-slip fault planes. In view of the regional structural grain in the Rwamagana-Musha-Ntunga area, this corresponds with abundant N20W-oriented pegmatites and quartz veins. The reactivation is strongly related to the lithology of the host rocks. The Musha Formation, which mainly consists of decimeter- to meter-scale lithological alternations of metapelite, metasiltstone and metasandstone, represents the most suitable environment for bedding reactivation. This is reflected in the predominance of bedding-parallel pegmatites and quartz veins hosted by the Musha Formation. Strike-parallel joints were mainly observed in the competent lithologies. The second controlling factor is related to the regional post-compressional stress regime. New joints initiated upon emplacement of the pegmatites and quartz veins. The orientations of these joints are influenced by the regional stress regime and resulted in steep EW-oriented pegmatites and quartz veins in the Rwamagana-Musha-Ntunga area. The pegmatites and quartz veins are interpreted as being initiated upon emplacement under influence of the prevailing regional stress regime. This post compressional stress regime is characterized by a subvertical maximum compressive stress. (C) 2017 Elsevier Ltd. All rights reserved.

The Mesoproterozoic Karagwe-Ankole Belt (KAB) extends from Burundi over Rwanda and NW-Tanzania to S-Uganda (Central Africa). The integration of the metamorphic and magmatic evolution of this orogenic belt in a consistent geodynamic framework is still controversial. Additionally, geochronological information on the deformation phases is limited. This tectono-metamorphic model is, however, a crucial component in the understanding of the Mesoto Early Neoproterozoic mineralization processes.

Near the village of Mousny, Belgium, a peculiar massive quartz occurrence, composed of multiple large, >m(3)-size, bodies of milky quartz can be found at the locality known as "Les Blancs Cailloux". Strikingly, the quartz bodies contain elongated, cleaved, host-rock fragments, still oriented parallel to the regional cleavage attitude. A detailed petrographical, microstructural and mineralogical study of the vein quartz and a geochemical analysis of fluid inclusions has revealed that the Mousny massive quartz occurrence is genetically linked to the regionally common cleavage-parallel quartz veins. They both show a fluid evolution typical of the metamorphic fluids in the central, epizonal part of the High-Ardenne slate belt. While the cleavage-parallel veins can be considered to result from mode I extensional fracturing, the genetically linked massive quartz occurrence is seen as being formed in a dilational jog. Within the late-orogenic context of the High-Ardenne slate belt, we favour a model in which the dilational jog is comprised within a weakly south-dipping, extensional shear zone, related to the late-orogenic extensional destabilization of the slate belt, causing a transient enhancement of the structural permeability in this low-permeability mid-crustal environment. The Mousny massive quartz occurrence may in this respect be exemplary for massive quartz occurrences throughout the High-Ardenne slate belt.

Regional mapping and a detailed geometric analysis of complex, mixed brittle-ductile, fold-related accommodation structures, along the well-exposed banks of the Lesse river between Redu and Daverdisse (Belgium), reveal that the finite strain in the predominantly incompetent Lower Devonian rock sequence in the northwestern part of the High-Ardenne slate belt deviates from pure flattening and approximates plane strain. This finite strain is materialised by different manifestations of non-cylindrical folding, i.e. regional en-echelon and periclinal fold geometries, mesoscale non-cylindrical folds with hinges showing variable plunges, oblique flexural slip and locally a non-axial planar, transecting cleavage. The observed non-cylindrical folding fits in the regional framework of the Meuse Valley Recess, a transpressional corridor in the Ardenne allochthon that developed on top of a buried, buttressing oblique ramp in the pre-structural basement. Differential propagation in the overriding Ardenne allochthonuous domain to the east and west of this buttressing oblique ramp led to a component of lateral shortening on top of the ramp, resulting in the rotation of the overall structural grain and the development of en-echelon, non-cylindrical folds. Our study suggests that the Meuse Valley Recess can be continued towards the southeast, at least affecting the northern parts of the High-Ardenne slate belt.

An integrated structural, petrographic and microthermometric methodology has been applied on syn- to late-orogenic quartz veins from the High-Ardenne slate belt (Belgium) to define their relative timing. The quartz precipitates, which do not show any mutual cross-cutting relationships, represent the meso-scale brittle accommodation during fold initiation, amplification and locking. Crystal-plastic deformation structures and P-T trapping conditions indicate that the different processes accommodating folding occurred in a progressive manner along a retrograde deformation path, associated with the gradual exhumation of the slate belt from ca. 7.5 to 6 km depth. Successive veining occurred from peak metamorphic conditions (ca. 300 degrees C and 190 MPa), measured in extrados veins, to subsequent lower P-T conditions in the periphery of a lenticular vein (ca. 275 degrees C and 180 MPa), late-orogenic saddle reef filling (ca. 245 degrees C and 160 MPa), and the core of a lenticular vein (ca. 220 degrees C and 150 MPa). Open-cavity growth and fluid-assisted brecciation indicate that veining occurred under overpressured fluid conditions. It is therefore fair to assume that the High-Ardenne slate belt acted - at least episodically - as a mid-crustal overpressured fluid reservoir, not only in the earliest and latest stages, but also during the main stage of orogeny. (C) 2013 Elsevier Ltd. All rights reserved.