Chemo-hydrodynamic patterns and instabilities in giant hydothermal ore systems

[Abstract] Although a large volume of research on the formation of giant ore deposits exists in the literature, two fundamental questions remain unanswered: 1). what leads to the highly localized and irregular patterns of mineral distribution? 2). why is there such a huge concentration difference of minerals between ore bodies and their crustal surroundings? The traditional way of describing such mineralizing systems is on a case-by-case basis and the linear equilibrium theory is applied which assumes only one final system state. Such an approach fails to explain most of the important characteristics of mineralising systems such as the existence of large spatial gradients in chemical potentials, paragenetic sequences and zoned mineral assemblages at all spatial scales.

Instead of concentrating on one particular ore body or one specific mineral type, this research is concerned with the general physical and chemical processes involved in the genesis of giant ore bodies. In linear systems, the principle of superposition holds whereas in nonlinear systems, completely different changes in system behaviour can take place when the controlling parameters pass some critical values. In this research, nonlinear methods and non-equilibrium approaches are adopted to study the chemo-hydrodynamic patterns generated by the coupled nonlinear reaction-diffusion-advection process in open hydrothermal mineralising systems. Open mineralising systems, can exhibit a variety of system behaviours which are different from closed systems. Different chemical reactions have been studied under steady and chaotic flow regimes. The traditional studies of mineralization assume uniform residence time for mineral components, which is only the case in steady flow regimes. Chaotic flow will lead to the fractal distribution of residence time; therefore, it will give rise to new system behaviours different from those in steady flow. Numerical simulations have also been performed to investigate the complex interactions between chemical reaction, fluid/heat flow and diffusion at the ore body and grain scale in porous media.