Alteration zones can be created around a number of the structural features (faults, shear zones, plugs, dykes and unconformities), and are defined as either alteration haloes, where the pre-existing rock property values are enhanced or depleted, or as replacement zones, where the original rock property values ar replaced without regard for the original values. In either case the alteration profile varies as a function of distance from the structural feature, using a standard profile definition window, and where appropriate can be defined as occuring above and/or below the defining surface. Beyond the Alteration Distance, the rocks simply maintain their original values.

Rock properties in these zones are defined by the product of the original rock property value and the alteration index. This index is defined as a function of distance using the alteration profile window, with the Properties value set to Line or Curve. The specific geophysical rock property profile being defined is selected from the Current Graph menu list, and the Options window supplies specific scaling parameters.

Alteration Options Window

Rock properties in these zones are defined only by the alteration value. This value is defined as a step function as a function of distance using the alteration profile window, with the Properties value set to Square

As an example of how alteration haloes behave as compared to replacement zones, the post alteration susceptibility values for these two modes are compared in table and graph form with the alteration profile values and the original susceptibility as a function of distance away from a dyke, with an Alteration Distance set to 600m.