Deformation of rock, fluid pressures and hydrothermal deposits

Deformation pattern of rocks in earth's crust is effected by tectonic stress, fluid pressure and gravity of the overlying strata. And the composition of rock and the size and the direction of tectonic stress determine the deformation of rock, while its breakdown is controlled by the pre-existed fault. The hydraulic fracture of rock occurs when the fluid pressure increases, however, the conditions of hydraulic extension fracture are σ1-σ3<4T and Pf=σ3+T. With the increase of depth in earth, the deformation of rocks changes from brittle behavior to ductile behavior by the influence of geothermal gradient. As long as there is no effection of fluid overpressure, brittle-ductile transition of rock happens in about 15km in the crust, on the condition of 300~450 ℃. When the fluid pressure and the strain rate increase, the deformation of rock will change from ductile to brittle in the ductile region and the depth of brittle-ductile transition will increase. On the perspective of tectonic mineralization, the depth of the hydrothermal deposits formation are related to the fluid pressure, strain rate, fracture and fault, the permeability of medium and the temperature. The migration and gathering place of fluid, the depth of the ore-forming, position and the orientation of orebodies and the permeability of rock are all affected by the types and direction of rock fracture.