Moore, C.H., 1987, Simulation of natural geochemical systems using a coupled transport/reaction model: An evaluation using the fluorine zone of quartz-cassiterite greisens as an example: Indiana University, Bloomington, Ph.D. dissertation, 199 p.
A coupled transport/reaction model, REACTRAN, is used to model the formation of the fluorine zone of quartz-cassiterite greisens. A discussion of the greisen at Kougarok, Alaska, and other deposits establishes the alteration zoning sequence common to many greisens - a fluorine zone, followed by a boron zone, and then an iron-silicate zone as one moves away from the intrusion. This large-scale zoning is attributable to the chemical evolution of the greisenizing fluid as well as to temperature gradients in the system. In the fluorine zone, mineralogical zoning is also commonplace, one such zonation being fluortopaz + cassiterite + muscovite + albite + feldspar. The development of this zonation is simulated using the REACTRAN computer code. Because many of the data required for the model are unknown (e.g. rate constants, equilibrium constants, fluid chemistry, etc.), they are treated as parameters and their values determined by comparing the results of simulations comparing them to observations of the natural system. A parameter space that gives good agreement is found and, by simulating the evolution of the system over relatively small ranges of values of these parameters, their relative importance is evaluated. It is clear that evolution in even the simplified system considered is controlled by complex interactions among processes and reactions that result in a network of feedback loops. It is the relative strengths of these loops that ultimately determine the system evolution in time. Because the model does not presently include all the possible species and processes that may be occurring in the natural system, it is necessary to use 'effective' values for some of the system parameters. These effective values allow for the model system to maintain an overall distribution of species that corresponds closely to the natural system. The effectiveness and necessity of using a coupled transport/reaction model that incorporates nonequilibrium process in simulating natural geochemical systems is demonstrated and this work provides a framework for using such models.
Theses and Dissertations
