1Hobbs, Bruce; 2Ord, Alison
1CSIRO, Perth Australia, 2The University of Western Australia, Perth, Australia
We address the question: Does the formation of giant ore hydrothermal deposits involve different process to the formation of average sized ore deposits? We draw analogies with the processes involved in mineralising systems with those used to explain the formation of rogue waves in oceanography and nonlinear optics and of tropical cyclones. Giant ore bodies constitute the tails of “fat tailed” distributions, or lie off the end of such distributions. It is important to distinguish between deposits that belong to a self-similar system (referred to as black swans by Sornette), and those that exceed what is expected from such a distribution (Sornette’s dragon-kings). It is proposed that similar processes operate for all members of a black swan distribution, and different processes operate via a phase transition for those that differ from the rest of the distribution. The nonlinear coupling between chemical reactions, deformation and permeability generation is discussed as a mechanism for forming regions of the Earth’s crust with anomalously high permeability. This nonlinear coupling between chemical reactions and deformation is identical to the physics used to explain rogue waves, tropical cyclones and dragon-kings. Thermodynamic arguments suggest the probability distributions for ore bodies at regional and microstructural scales should be fat tailed Fréchet distributions and it is shown that examples from natural mineralising systems conform to these distributions at a range of spatial scales. The implications for mineral deposit prediction and assessment using log-normal distributions and Zipf’s law are discussed together with the implications for kriging.
Bruce Hobbs is a structural geologist. His present interests are in applying the tools developed for nonlinear dynamical systems over the past 50 years or so to large data sets on alteration assemblages, deformation and mineralisation in mineralising systems in order to extract information of relevance to metal discovery.