Dissolution of deep carbonate rocks by fluid mixing: a discussion based on reactive transport modeling

The geochemical processes proposed until now to explain the formation of cavities in deep carbonates are difficult to reconcile with observations. We propose a mixing model of hydrothermal solutions equilibrated with carbonate. Through numerical reactive transport simulations, we observe that chemical mixing of hydrothermal solutions can generate a zone of host:rock dissolution and another of minor calcite precipitation. Variations in relative fluid velocities, pH or S content may result in the growth of the precipitation zone with respect to the dissolution one. This explains the finding of dissolution cavities in carbonate rocks with subsequent filling by carbonate minerals. (C) 2003 Elsevier Science B.V. All rights reserved.