This thesis describes preliminary two- and three-dimensional modelling of mass and heat transport of hot, molten magma in crustal intrusions and of the associated thermally induced flow of groundwater contained in the surrounding country rock. The aim of such modelling is to create a tool with which to predict the location of mineral deposits formed by the transport and subsequent precipitation of minerals dissolved in the convecting groundwater. The momentum equations (Navier-Stokes equations), continuity equation and energy equation are used in conjunction with specially constructed density and viscosity relationships to govern the mass and heat transport processes of magma and groundwater. Finite element methods are used to solve the equations numerically for some simple model geometries. These methods are implemented by a commercial computer software code which is manipulated with a control program constructed by the author for the purpose. The models are of simple two- or three-dimensional geometries which all have an enclosed magma chamber surrounded completely by a shell of country rock through which groundwater is free to move. Modelling begins immediately after the intrusive event when the magma (in most cases rhyolitic) is at its greatest temperature. Heat is allowed to flow from the magma into the country rock causing thermal convection of the groundwater contained therein. The effect of the country rock as a porous medium on the flow of groundwater is modelled by including a distributed resistance term in the momentum equation. The computer code that controls the modelling is such that adaptions made to the models to represent real physical intrusive systems are trivial. Results of the research at this stage allow approximate prediction of the location of mineral deposits. Enhanced predictions can be made by effecting improvements to the models such as a more detailed representation of chemical processes, adaption of the computer code to allow multiple injections of magma and the modelling of frozen magma as a porous medium which admits the flow of groundwater.

This thesis presents results of two-dimensional finite element modelling of a magma chamber surrounded by country-rock containing a section of high permeability. The high permeability section in the country-rock simulates structure that is predominant in controlling the groundwater convection pattern and resulting mineral deposits. The models have analogies in nature: for instance the gold mines in the Massif Central of France, the Pogo mine in Alaska and the Pilgrim's Rest gold field in South Africa. This is a complicated coupled system involving fluid flow and heat transfer under extreme conditions. The magma in the chamber convects and as it cools the heat liberated causes convection in the groundwater contained in the surrounding country-rock. This convection in turn affects the rate of liberation of heat from the magma. The software used for the modelling, FLOTRAN, is the computational fluid dynamics component of the commercial ANSYS package. The results obtained describe in detail the flow pattern in the magma chamber, the country-rock and high permeability section thereof. During the cooling of the magma chamber the groundwater convects more vigorously in the high permeability section than elsewhere, and a convection cell is seen forming within this region. This provides a mechanism for hydrothermal formation of valuable mineral deposits in the structure near a magma chamber. It is found that the relationship between the velocity of the flow in the cell and the temperature of the magma chamber is well represented by a first order linear differential equation, providing a simple understanding of this process, / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

Most downhole tools in use today measure properties immediately adjacent to the borehole, and as such, only a small portion of the subsurface volume is known with any degree of certainty. When dealing with geologic situations which are characteristically heterogeneous, the engineer often requires more information than what present tests can provide. Tomography is an in-situ testing method that allows the generation of a two dimensional subsurface image by reconstructing material property variations between boreholes. It is essentially a solution to the inverse problem where signals are measured and, through computer manipulation, are used to infer material contrasts in the subsurface. For the purposes of this thesis, a two dimensional configuration is used to demonstrate and evaluate the tomographic technique with source and receiver locations positioned at intervals down adjacent and nearly vertical boreholes. Both iterative and direct matrix solution methods are used to evaluate the use of seismic and groundwater flow data for subsurface tomography. The iterative methods include a variation of the classical algebraic reconstruction technique (CART), a modified version of the ART algorithm (MART), and a modified version of the ART algorithm using the Chebyshev norm criterion (LART). The purpose of the iterative tests is to determine the best algorithm for signal reconstruction when data noise and different damping parameters are applied. The matrix methodologies include a constrained L¹ linear approximation algorithm and singular value decomposition routines (SVD). These methods solve the set of linear equations (Ax = b) which the tomographic techniques produce. The purpose of this stage of testing is to optimize a direct method of solution to the sets of linear equations such that different forms of anomaly can be discerned. Numerous synthetic seismic and groundwater data sets are used by both iterative and matrix algorithms. Seismic test data sets are generated by calculation of transit times through materials of known seismic velocity. Groundwater test data sets are generated by drawdown analyses and finite element procedures. All algorithms demonstrate a reasonable ability at reconstructing sections which closely re-sembled the known profiles. Vertical anomalies, however, are not as well defined as horizontal anomalies. This is primarily a result of incomplete cross-hole scanning geometry which also affects the rank and condition of the matrices used by the direct forms of solution. The addition of Gaussian noise to the data produces poor reconstructions regardless of the type of algorithm used. This emphasizes the fact that tomographic techniques require clear and relatively error-free signals. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Inverse modeling of aquifers usually involves identification of effective parameters such as transmissivities over a finite number of subregions, or zones. Theoretical restrictions on the maximum size of a zone for which such effective transmissivities can be properly defined and the desire to obtain a good resolution of the spatial variability of transmissivity may suggest that the aquifer be divided into numerous small zones. Considerations of parameter identifiability, on the other hand, may require that the number of unknown transmissivities be limited. To satisfy both requirements, an inverse approach has been developed in which the number of zones can be as large as deemed necessary on the basis of hydrogeological considerations. However, instead of trying to estimate a similar number of transmissivities, a smaller number of surrogate parameters, which are defined as linear combinations of the original log transmissivities, is estimated. The optimum number and definition of the surrogate parameters are determined through a singular value decomposition of a matrix arising from the linearization of the inverse problem. A "resolution matrix" and an "information density matrix" can also be obtained from the singular value decomposition. The resolution matrix is indicative of parameter identifiability and is valuable in deciding whether specific log-transmissivity zones should be lumped with their neighbors or left intact. The information density matrix shows how well the model can reproduce each measured hydraulic head value and may be used to determine the relative worth of each datum point for parameter estimation. This, in turn, may suggest discontinuing the collection of certain data and/or starting to collect data at other points in the aquifer. The methodology is illustrated by using data from the Avra Valley aquifer of southern Arizona.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 123-132). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1982. / Includes bibliographical references (leaves 58-61).

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1986. / Includes bibliographical references (leaves 136-139).

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1997. / Includes bibliographical references (leaves 311-317).

Thesis (M.S. in civil engineering)--Washington State University, December 2007. / Includes bibliographical references (p. 45-48).