Large-scale strike-slip faults are fundamental tectonic elements of the continental lithosphere. They constitute plate boundaries (continental transforms), separate terranes with contrasting geological histories within accretionary orogens, or accommodate heterogeneous deformation in intracontinental settings. In ancient orogens, where deeper levels of the crust are exposed, these faults are expressed as shear zones materialized by up to tens of km-wide mylonitic belts. The Borborema shear zone system in northeastern Brazil is one of the largest and best-exposed intracontinental strike-slip shear zone systems in the world, cropping out over 250,000 km². Here, we review its main geophysical, structural, petrologic, and geochronologic characteristics and discuss the factors controlling its development. This complex continental scale shear zone system is composed of a set of NE- to NNE-trending dextral shear zones from which there are two major E-trending dextral shear zones with horse-tail terminations into the transpressional belt branch, as well as several smaller E-trending dextral and NE-trending dextral and sinistral shear zones. The major shear zones are marked by extensive linear or curvilinear magnetic gradients, implying their continuation at depth. The major shear zones are materialized by migmatite to amphibolite-facies mylonites, but the entire system shows evidence of late deformation at lower temperatures. The system developed during the late stages of the Neoproterozoic Brasiliano (Pan-African) orogeny (mainly from 590 to 560 Ma), postdating by more than 20 Ma the main stage of contractional deformation. Localization of strike-slip shearing in this intraplate setting was controlled by rheological contrasts between blocks with distinct Paleoproterozoic histories, the presence of preorogenic Neoproterozoic rifts, the craton geometry, and zones of enhanced magmatic activity, highlighting the importance of rheological heterogeneity in controlling shear zone nucleation and evolution.

The integration of geological data obtained through fieldwork, remote sensing and airborne geophysics has been shown to be efficient in creation of precise geological maps. The Vieirópolis region, sited in the west of the Rio Grande do Norte Subprovince of the Borborema Province, is characteristically made up of rocks intensely deformed by transcurrent shear zones and late brittle structures which control the mineralization of gemmological and industrial minerals. ASTER GDEM and airborne geophysical images (magnetometry and gamma-ray spectrometry) were used in order to enhance the geological knowledge of this region and to facilitate the identification and delimitation of structures and lithologies mapped during stages of fieldwork. Thus, a geological map on a scale of 1:50,000 was achieved, made up of six main lithological units and three new shear zones (Vieirópolis, Lastro and São Pedro), as well as the NE-SW-trending Portalegre Shear Zone. Within the newly mapped structures, the Vieirópolis Shear Zone stands out due to its expressiveness. Aeromagnetometry data suggest that this zone originated on the edge of the Brejo das Freiras Subbasin, part of the Portalegre Shear Zone System. NW-SE, ESE-WNW and E-W lineaments were correlated to lesser extent brittle structures which sometimes transversely cut the regional foliation, allowing pegmatite fluids to rise. The RGB ternary composition map (K, eTh, eU) also corroborates the presence of these structures, besides helping to determine lithological units. In this case study, the integration of direct and indirect data showed to be essential for the understanding and producing of local geological map.

The Paraná deposit, located at Southwestern Rio Grande do Norte state, in Brazil, is one of the few emerald deposits found at Borborema Province. The mineralization occurs in phlogopite schists and actinolite-phlogopite schists associated with pegmatites and albitites within the Portalegre Shear Zone. Unlike other well-known Brazilian emerald deposits, the mineralogy of Paraná emeralds has remained poorly investigated for the last 40 years. In this study, we conducted mineralogical characterization of theses emeralds through gemological testing, mineral chemistry, absorption and reflectance spectroscopy, and thermal analysis. The Paraná emeralds are bluish-green colored, characterized by high refractive index, several two-phase fluid inclusions and mica is the main mineral inclusion. Electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry analyses detected the presence of Fe²⁺ (0.43-1.94 wt.% FeO) and Cr³⁺ (0.04-0.14 wt.% Cr₂O₃) as the main chromophores replacing octahedral Al³⁺ in the crystal structure. In addition, substantial amounts of MgO (0.40-2.72 wt.%), Na₂O (0.50-1.81 wt.%), and Cs₂O (0.07-0.44 wt.%) were also identified. The main causes for its coloration were attributed to Cr³⁺ absorption features in visible spectral range, which were corroborated by absorption and reflectance spectra. The presence of types I and II H₂O at channel-sites was recorded in Fourier-transform infrared spectra and demonstrated by dehydration processes observed in different thermal and thermogravimetric analyses.

We present a combined analysis of airborne geophysical data (magnetics and gamma-ray spectrometry) and field aspects of Itapetim lode gold district region, aiming to identify structurally deformed and hydrothermally altered zones, which are suggestive of gold mineralized sectors. The main geophysical lineaments are oriented in the NE-SW and E-W directions and display a clear correlation with the major gold-bearing structures in the region. In the magnetic maps, the key pathfinder for gold occurrences is their association with strongly magnetized areas positioned along the Itapetim Shear Zone and outer contour of Teixeira Batholith. In the field, such structures are materialized in protomylonitic and mylonitic rocks that present evidence of ductile and brittle deformation, whereas kinematic criteria are suggestive of a transpressional tectonic regime. In addition, the main radiometric pattern is characterized by K enrichment, which is correlated with a hydrothermal mineral assemblage dominated by quartz, potassium feldspar, and tourmaline. Based on the obtained data integration, we produced an integrative map and located ten new target areas of possible gold mineralization, which is correlative to other well-known lode deposits in Northeast Brazil and Africa.