Lester,D.R., Ord,A. and Hobbs,B.E.(2012): The mechanics of hydrothermal systems: II. Fluid mixing and chemical reactions. Ore Geology Reviews, 49, 45-71.

『熱水系のメカニクス:2 流体混合と化学反応』


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


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