A view of orogenic gold deposits as nonlinear systems: Nonlinear analysis of data

Ord, Alison1, Hobbs, Bruce2

1The University of Western Australia, Perth, Australia, 2CSIRO, Perth Australia

Despite many studies of orogenic gold systems, the underlying processes involved in their formation and in defining their location remain enigmatic. This arises because such processes are multiscale and nonlinear so that patterns of alteration and mineralisation are apparently irregular and unpredictable. The goal of a nonlinear dynamical analysis of spatial data is to extract the dynamics of the underlying nonlinear and multiscale physical and chemical processes that produced these data. We review nonlinear analysis methodology and explore hyperspectral and gold assay data for a drill-hole in an orogenic gold system. The analysis is non-parametric and purely data driven. We use recurrence, cross- and joint-recurrence plots to extract the invariant measures of the system including the embedding dimension, the first positive Lyapunov exponent and the entropy and construct the attractor for the mineral distributions. The resulting dynamical model is tested using nonlinear prediction algorithms. Cross recurrence analysis shows strong spatial correlations of gold with carbonates and weaker correlations with phengitic micas and chlorite. Joint recurrence analysis reveals that all parts of the system are part of the same dynamical attractor and hence parts of the same physical-chemical system. We speculate on the coupled processes, compatible with the nonlinear analysis, responsible for the mineralising system. The overall aim is to constrain the structure and organisation of the coupled non-equilibrium dynamics that define this system. We propose that autocatalytic reactions associated with quartz and carbonate deposition control pH variations responsible for gold deposition and present a new view of mineralising systems.


Alison is a structural geologist interested in the mechanics of hydrothermal systems, computer modelling of coupled deforming systems with heat and fluid transport and the thermodynamics of chaotic systems. She aims to apply the tools developed for nonlinear dynamical systems to quantify and fingerprint various classes of mineralising systems

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