NEWGRES - A TURBO PASCAL PROGRAM TO SOLVE A MODIFIED VERSION OF GRESENS HYDROTHERMAL ALTERATION EQUATION

Chemical compositions of altered rocks cannot be compared directly to the compositions of the unaltered parent rocks because of volume changes attendant on alteration. In order to make such a comparison, the observed chemical changes must be corrected for volume changes, usually by identifying immobile elements that are conserved during alteration. Gresens' equation can be used to estimate the volume changes, and subsequently calculate the chemical changes. A modified version of Gresens' hydrothermal alteration equation has been derived that expresses metasomatic losses and gains as a ratio of component weights rather than a weight difference. The resulting equation is more applicable to comparison of the behavior of components during hydrothermal alteration. In graphical presentations loss of components can be given the same visual weight as component gain. The programs GRES (for Gresens' equation) and NEWGRES (for the modified equation) enable rapid modeling of chemical mass balance during hydrothermal alteration, with the ability to rapidly compare the outcome of selecting different parent rocks or different immobile components. © 1990.