Fluid pumping: Some exploratory numerical models

Abstract

The concept of fluid pumping evolved from considerations of fluid behaviour within and surrounding faults and shear zones, particularly associated with earthquake initiation and propagation. Further, the interpretation of specific vein textures as originating from a crack-seal mechanism requires precipitation of material during pumping cycles. We explore here a new simple model for fluid pumping initiating within a dilatant, pressure dependant material, and the mechanical consequences of such a model, including the predicted behaviour of a fluid within the SiO2-H2O system. Changes in various properties such as permeability and mechanical properties are allowed according to rules based on defined geological processes. For example, porosity may increase with increasing shear and dilatancy of the rock, and both porosity and permeability decrease when and where the rock ‘seals’ as a result of pressure decrease and the resultant precipitation of SiO2. Histories of any variable may be explored for any part of the model. We may therefore test in a quantitative manner hypotheses for fluid pumping, and the deposition of quartz, and ultimately gold, in a deforming rock mass. Through exploring the feedback links between deformation, fluid flow, chemical transport, thermal transfer, we have the opportunity to test conceptually and quantitatively the various hypotheses for the formation of world class ore deposits.