Seismogenic Nature of Fluid-Dynamic Structural Parageneses of the Uryakh Gold Ore Field (Northeastern Transbaikalia)

Abstract

New data on the geological structure and ore-bearing structural parageneses of the Uryakh gold ore field are presented. The formation of the deposit occurred in dynamic shear regime along ore-controlling deep-seated faults of the Syulban fault system and faults of the system transverse to it. The interaction of two duplex shear systems resulted in the block structure of the ore field. Tectonophysical methods have established the individual development of tectonic blocks during the period of gold-bearing fluid input in a seismically active regime. The specific features of the formation of ore-bearing fracture–fault structural parageneses in the blocks resulted from the change in the seismic regime under the action of pressure and gas-saturated fluids. The parameters of the fluid system were determined by fluid inclusion studies in quartz. An unstable variable compression–extension regime of the early phase of seismic activity led to the formation of hybrid structural parageneses under the influence of stresses of damping shear and injective hydrodynamic stress. Variations in the stress–strain state of the medium in this phase correspond to a transient seismic regime and are consistent with variations in the thermobarometric parameters of the fluid system. In the late phase of seismic activity, a stable uniaxial tension regime with a superlithostatic fluid pressure occurred, which caused brittle deformations independent of slip along the fault. The centroid mechanism of such deformations, which is rarely found in the dynamic regimes of hydrothermal deposits, ensured the formation of structural parageneses unusual for shear zones, which resulted in a different combination of structural and morphological types of orebodies in the blocks.