The geological setting of lode-gold deposits in the central southern Urals: a review

The late-Paleozoic Uralides represent one of the largest lode-gold metallog enic provinces in the world. In the southern Urals, gold distribution is he terogeneous and is confined mainly to two tectonostratigraphic zones, namel y the Main Uralian fault and the East Uralian zone. The important lode-gold districts within and in the immediate hangingwall of the first-order crust al suture of the Main Uralian fault are characterized by a complex tectonic history of earlier compressional tectonics involving thrusting, folding an d reverse faulting and later transcurrent shearing. Gold mineralization is hosted by second- and third-order brittle to brittle-ductile strike-slip fa ults that developed late during the kinematic history of the Main Uralian f ault. Strike-slip reactivation of earlier compressional structures was rela ted to the late-stage docking of the passive margin of the East European pl atform with island-are complexes of the southern Urals, an event that is te ntatively related to changes in plate motion during the final stages of ter rane accretion during the upper Permian and lower Triassic. Gold mineraliza tion was controlled by the permeability characteristics of the hydrothermal conduits, as well as by competence contrasts and geochemistry of the mainl y volcanic host rocks. Mineralization occurred at relatively shallow crusta l levels (2-6 km) and largely post dates peak-metamorphism of the host rock s. The large and very large (up to 300 to Au) gold deposits of the East Ura lian zone are hosted by upper-Paleozoic granitoid massifs. Gold mineralizat ion is temporally associated with the main phase of regional-scale compress ional tectonics and granite plutonism during the upper Carboniferous and lo wer Permian. Controlling structures have a dominantly east-west strike and occur as hybrid shear-tensional vein systems in competent granitoids subjec ted to east/west-directed regional shortening. Deformation textures and alt eration mineral assemblages indicate lower-amphibolite-facies conditions of mineralization close to peak metamorphic conditions that are associated wi th the mid-Permian regional metamorphism and tectonism. Gold deposits in th e southern Urals are, therefore, polygenetic and are temporally and genetic ally distinct in each of the two major mineralized tectonostratigraphic zon es of this well-preserved collisional orogenic belt, The different timing o f ore fluid generation and fluid discharge is interpreted to be the result of the different tectonic, metamorphic and magmatic evolution of terranes i n the southern Urals.