Regional-scale pressure shadow-controlled mineralization in the Príncipe Orogenic Gold Deposit, Central Brazil

• Classification of the Príncipe Gold Deposit as orogenic by fieldwork and analyses
• Paleoproterozoic lithological assemblage reworked in the late Neoproterozoic
• Transbrasiliano Strike Slip System responsible for the strong structural control
• Ore trapping along quartz veins inside a regional-scale auriferous pressure shadow

The Príncipe Gold Deposit, situated in the Natividade Gold District, resulted from establishment of the regional Transbrasiliano Strike–Slip System during the late Neoproterozoic Brasiliano Event. The host rocks, however, were formed in the Paleoproterozoic (with Sm–Nd model ages from 2250 to 2500 Ma), therefore the Príncipe Gold Deposit is epigenetic. The local lithological association is a tonalitic–granodioritic suite formed in an island arc environment that later experienced continental collision tectonics, leading to the intrusion of the peraluminous Príncipe Granite (with an age of 2169 ± 42 Ma by zircon U–Pb). During the Neoproterozoic, these units underwent deformational greenschist facies metamorphism and hydrothermal alteration, forming metamorphic tectonites inside the Príncipe Granite and hydrothermally altered rocks at the northern termination of the granite, where the Príncipe Gold Deposit is located.A strong structural control is identified in the deposit, with N10°W–N20°E-trending brittle–ductile shear zones that are visible at all scales, from thin sections to regional satellite images. These shear zones played an important role in the formation of the deposit, acting as pathways that promoted a channelized fluid flow to metal precipitation sites. Hydrothermal alteration processes of different grades occur along these structures, mainly characterized by saussuritization, biotitization, chloritization, sericitization, carbonatization, silicification and sulfidation reactions, producing a neoformed mineral assemblage. The Príncipe Granite acted as a regional-scale porphyroclast for migration of the hydrothermal solutions as well as deformation, forming two pressure shadows that acted as structural traps for the ore. As stress release zones, these structures concentrated hydrothermal solutions during seismic fault movement events under a transpressive regime. They also changed the physicochemical conditions in the fluid by abruptly reducing the pressure and increasing the fluid–rock interaction rate, producing a structural framework characterized by a pervasively interconnected system of discontinuous and anastomosed quartz–carbonate–sulfide–gold-veins.Fieldwork, petrographic analysis and mineral chemistry characterization suggest that the fluid had an aqueous–carbonic nature and low salinity values. Thermometric studies suggest that gold mineralization occurred between 250 °C and 400 °C. Stable isotopes of S, C and O indicate a metamorphic source for the fluid. Whole rock geochemistry and microprobe studies highlight hydrothermal alteration processes involving Fe, Ca, Mg, K, Na, Au and Ag metasomatism.The Príncipe Gold Deposit belongs to the orogenic class, but it is distinguished from other orogenic-type occurrences in the Natividade Gold District and from most orogenic deposits of the world for not being located along a shear zone. Instead, it is situated within a regional-scale auriferous pressure shadow that was brought about by a short-lived pressure drop during the Brasiliano Cycle.