MODELING REACTIVE GEOCHEMICAL TRANSPORT IN NATURAL FRACTURED ROCK SYSTEMS OVER GEOLOGICAL TIME

摘要

Reactive fluid flow and geochemical transport in natural fractured rock systems has been of increasing interest to investigators in areas of geoscien-ces such as mineral deposits, sedimentary diagenesis, and fluid-rock interactions in hydrothermal systems. Validation of numerical models for natural and anthropogenic (engineered) systems may differ markedly. In anthropogenic systems such as contaminant transport and nuclear waste repositories, models must be validated based on measurements of state variables such as pressure, water saturation, and chemical concentration, and the scientific relevance of modeling must be in prediction. For natural phenomena, the geological relevance of modeling often is in hypothesis testing, because natural processes and geochemical systems may involve too many complications and uncertainties to allow for quantitative prediction. Natural mineral systems are characterized by the abundance and distribution of primary and secondary mineral phases, and by the composition of fluid phases (aqueous, gas). Often it is the presence or absence of certain minerals that provides clues to the specific physical and chemical processes and conditions during the evolution of the system. In this sense empirical tests of the accuracy of geochemical modeling are of a more qualitative nature for natural systems. If modeling can find an unambiguous answer to a simple question which is well-posed, then something can be learned. The test of numerical results is by comparison with known patterns, sequences and processes from natural systems, which may be qualitative rather than quantitative in terms of mineral abundances. Therefore, in this paper we use the term "observation" instead of "measurement", and we intend to bridge the gap between observation and modeling.