『Abstract
In the accompanying paper, Part I, hydrothermal mineralising systems
are considered as open chemical reactors that operate far from
equilibrium to develop an exothermal alteration system with veining
and brecciation, followed by competition between endothermic mineralisation
and exothermic mineral reactions. In this sequel paper, we examine
the interplay of these processes with fluid transport and the
impact upon mineral deposition. Chemical reaction and flow in
porous media admit two distinct mechanisms which result in significantly
accelerated mixing. First, gradients in physical parameters such
as chemical potential, fluid density and surface tension generate
flow instabilities which form fluid/chemical mixing machines that
propagate with the reaction front. Second, so-called chaotic advection,
a behaviour in which fluid particles follow chaotic trajectories,
arises inherently from Stokes flow in open porous networks as
a result of the complexity of the pore geometry. For pore length-scales
greater than 〜1 mm, these mechanisms significantly enhance mixing
and hence metal/sulphide deposition. Furthermore, chaotic advection
can also alter qualitative characteristics such as stability or
speciation of non-equilibrium chemical reactions, with significant
implications for enhanced mineralisation rates. Such interactions
between chemical reaction and fluid advection generate mineral
deposits with multifractal spatial signatures similar to those
observed in the field. Such multifractal signatures render the
spatial distributions non-ergodic, a fact which process based
geostatistics must take into account.
Keywords: Hydrothermal systems; Chaotic mixing; Open flow systems;
Flow controlled systems; Mineralisation; Ergodicity; Multifractals』
Contents
1. Introduction
2. Governing equations and definition of terms
2.1. Governing equations
3. Fluid mixing and chaotic advection
3.1. Chaotic advection in laminar flow
3.2. Chaotic advection and dispersion
4. Chemical reactions, flow instabilities and fluid mixing
5. Pore/fracture geometry and fluid mixing
5.1. Chaotic advection and dispersion at the pore-scale
5.2. Chaotic advection and dispersion at the macro-scale
6. Chaotic advection and chemical reactions
6.1. Background
6.2. The advection-diffusion-reaction (ADR) systems
6.2.1. Dynamics of simple reactions
6.2.2. Simplified models of the ADR system
6.2.3. Chemical transitions induced by chaotic advection
6.3. Chaotic advection and reactions in open porous media flow
6.3.1. Properties of open flow systems
6.3.2. Autocatalysis in open flows
6.3.3. Competitive autocatalytic reactions in open flows
6.3.4. Bistable reactions in open flows
6.3.5. Reactions in 3D open flows
6.3.6. Reactions in non-hyperbolic open flows
6.4. Implications for hydrothermal systems
7. Discussion
8. Concluding remarks
Acknowledgements
Appendix
References