Chemical compaction, also known as pressure solution, involves dissolution along grain contacts and transport of solute to the adjacent pore space by diffusion. The driving force for diffusion is a gradient in chemical potential, therefore chemical compaction requires persistent gradients in chemical potential along grain contacts, in order to drive diffusion continuously. Such gradients exist in porous rocks because of the heterogeneous distribution of stress over the grain surfaces. The rate of chemical compaction depends on stress, fluid pressure, temperature, and the composition of the pore fluid, which itself depends on various processes that add or remove solute. An alternative model of chemical compaction invokes the effect of sheet silicates on pH to account for localized dissolution of grains adjacent to stylolites, or where sheet silicates are present along grain contacts. In this model, the rate of chemical compaction is independent of stress and fluid pressure, depending only on temperature. This model is untenable because the proposed mechanism cannot give rise to the persistent gradient in chemical potential required to drive diffusion. However, sheet silicates may increase the rate of chemical compaction because of their influence on dissolution and diffusion rates. The development of anisotropic fabrics as a result of chemical compaction, and the widespread occurrence of stylolites in carbonates as well as sandstones, are inconsistent with the pH model and provide strong support for the role of stress in chemical compaction.

Mineralization of brittle fault zones is associated with sudden dilation, and the corresponding changes in porosity, permeability and fluid pressure, that occur during fault slip events. The resulting fluid pressure gradients cause fluid to flow into and along the fault until it is sealed. The volume of fluid that can pass through the deforming region depends on the degree of dilation, the porosity and permeability of the fault and wall rocks, and the rate of fault sealing. A numerical model representing a steep fault cutting through a horizontal seal is used to investigate patterns of fluid flow following a dilatant fault slip event. The model is initialized with porosity, permeability and fluid pressure representing the static mechanical state of the system immediately after such an event. Fault sealing is represented by a specified evolution of porosity, coupled to changes in permeability and fluid pressure, with the rate of porosity reduction being constrained by independent estimates of the rate of fault sealing by pressure solution. The general pattern of fluid flow predicted by the model is of initial flow into the fault from all directions, followed by upward flow driven by overpressure beneath the seal. The integrated fluid flux through the fault after a single failure event is insufficient to account for observed mineralization in faults; mineralization would require multiple fault slip events. Downward flow is predicted if the wall rocks below the seal are less permeable than those above. This phenomenon could at least partially explain the occurrence of uranium deposits in reactivated basement faults that cross an unconformity between relatively impermeable basement and overlying sedimentary rocks.

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Mineral deposits are commonly hosted by small-displacement structures around jogs in major faults, but they are rarely hosted by the major fault itself. This relationship may be explained by time-dependent fracturing and healing in and around major faults and associated permeability evolution. A damage mechanics formulation is used here to explore the spatial-temporal evolution of damage in and around a fault following a fault-slip event. We show that regions of increased damage rate correspond to the location of mineral deposits and that these areas correspond to areas of aftershocks predicted by stress-transfer modeling. The fault itself enters a healing regime following the slip event; hence, it is expected to become less permeable than the fracture network outside the fault. Our results support the hypothesis that mineralization occurs in a fracture network associated with aftershocks; this may be due to the higher time-integrated permeability of the fracture network relative to the main fault.