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The Spatial and Temporal Distribution of the Metal Mineralisation in Eastern Australia and the Relationship of the Observed Patterns to Giant Ore Deposits

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The Spatial and Temporal Distribution of the Metal Mineralisation in Eastern Australia and the Relationship of the Observed Patterns to Giant Ore Deposits The Spatial and Temporal Distribution of the Metal Mineralisation in Eastern Australia and the Relationship of the Observed Patterns to Giant Ore Deposits A thesis submitted for the degree of Doctor of Philosophy May 2007 Larry J. Robinson School of Earth Sciences Principal Advisor Associate Professor Dr. Suzanne D. Golding Associate Advisor Senior Lecturer Dr. Richard Wilson Certificate of Originality I hereby certify that the work embodied in this thesis is the result of original research and has not been submitted for a higher degree at any other University or Institution. (Signed) Larry John Robinson ABSTRACT The introduced mineral deposit model (MDM) is the product of a trans-disciplinary study, based on Complexity and General Systems Theory. Both investigate the abstract organization of phenomena, independent of their substance, type, or spatial or temporal scale of existence. The focus of the research has been on giant, hydrothermal mineral deposits. They constitute <0.001% of the total number of deposits yet contain 70-85% of the world's metal resources. Giants are the definitive exploration targets. They are more profitable to exploit and less susceptible to fluctuations of the market. Consensus has it that the same processes that generate small deposits also form giants but those processes are simply longer, vaster, and larger. Heat is the dominant factor in the genesis of giant mineral deposits. A paleothermal map shows where the vast heat required to generate a giant has been concentrated in a large space, and even allows us to deduce the duration of the process. To generate a paleothermal map acceptable to the scientific community requires reproducibility. Experimentation with various approaches to pattern recognition of geochemical data showed that the AUTOCLUST algorithm not only gave reproducibility but also gave the most consistent, most meaningful results. It automatically extracts boundaries based on Voronoi and Delaunay tessellations. The user does not specify parameters; however, the modeller does have tools to explore the data. This approach is near ideal in that it removes much of the human- generated bias. This algorithm reveals the radial, spatial distribution, of gold deposits in the Lachlan Fold Belt of southeastern Australia at two distinct scales – repeating patterns every ~80 km and ~230 km. Both scales of patterning are reflected in the geology. The ~80 km patterns are nested within the ~230 km patterns revealing a self-similar, geometrical relationship. It is proposed that these patterns originate from Rayleigh-Bénard convection in the mantle. At the Rayleigh Number appropriate for the mantle, the stable planform is the spoke pattern, where hot mantle material is moving upward near the centre of the pattern and outward along the radial arms. Discontinuities in the mantle, Rayleigh-Bénard convection in the mantle, and the spatial distribution of giant mineral deposits, are correlative. The discontinuities in the Earth are acting as platforms from which Rayleigh-Bénard convection can originate. Shallow discontinuities give rise to plumelets, which manifest at the crust as repeating patterns ranging, from ~100 to ~1,000 km in diameter. Deeper discontinuities give rise to plumes, which become apparent at i the crust as repeating patterns ranging from >1,000 to ~4,000 km in diameter. The deepest discontinuities give rise to the superplumes, which become detectable at the crust as repeating patterns ranging from >4,000 to >10,000 km in diameter. Rayleigh-Bénard convection concentrates the reservoir of heat in the mantle into specific locations in the crust; thereby providing the vast heat requirements for the processes that generate giant, hydrothermal mineral deposits. The radial spatial distribution patterns observed for gold deposits are also present for base metal deposits. At the supergiant Broken Hill deposit in far western New South Wales, Australia, the higher temperature Broken Hill-type deposits occur in a radial pattern while the lower temperature deposits occur in concentric patterns. The supergiant Broken Hill deposit occurs at the very centre of the pattern. If the supergiant Broken Hill Deposit was buried beneath alluvium, water or younger rocks, it would now be possible to predict its location with accuracy measured in tens of square kilometres. This predictive accuracy is desired by every exploration manager of every exploration company. The giant deposits at Broken Hill, Olympic Dam, and Mount Isa all occur on the edge of an annulus. There are at least two ways of creating an annulus on the Earth's surface. One is through Rayleigh-Bénard convection and the other is through meteor impact. It is likely that only 'large' meteors (those >10 km in diameter) would have any permanent impact on the mantle. Lesser meteors would leave only a superficial scar that would be eroded away. The permanent scars in the mantle act as ‘accidental templates’ consisting of concentric and possibly radial fractures that impose those structures on any rocks that were subsequently laid down or emplaced over the mantle. In southeastern Australia, the proposed Deniliquin Impact structure has been an 'accidental template' providing a 'line-of-least-resistance' for the ascent of the ~2,000 km diameter, offshore, Cape Howe Plume. The western and northwestern radial arms of this plume have created the very geometry of the Lachlan Fold Belt, as well as giving rise to the spatial distribution of the granitic rocks in that belt and ultimately to the gold deposits. The interplay between the templating of the mantle by meteor impacts and the ascent of plumelets, plumes or superplumes from various discontinuities in the mantle is quite possibly the reason that mineral deposits occur where they do. ii TABLE OF CONTENTS 1 INTRODUCTION ......................................................................................................................................... 1 1.1 OBJECTIVE AND SCOPE........................................................................................................................... 1 1.2 THE MINERAL DEPOSIT MODEL............................................................................................................. 5 1.3 ORGANISATION OF THE THESIS .............................................................................................................. 6 2 GENERAL SYSTEMS APPROACH TO MODELLING ..................................................................... 10 2.1 SYSTEMS THEORY AND THE GENERAL SYSTEMS APPROACH ............................................................. 12 2.2 COMPLEXITY, EMERGENCE, MODEL BUILDING, & SIMPLICITY .......................................................... 15 2.2.1 Complexity..................................................................................................................................... 15 2.2.2 Emergence..................................................................................................................................... 18 2.2.3 Model Building.............................................................................................................................. 21 2.2.4 Simplicity....................................................................................................................................... 25 2.3 FRACTALS, CHAOS THEORY, AND NONLINEAR DYNAMICS................................................................. 27 2.3.1 Fractals ......................................................................................................................................... 27 2.3.2 Chaos Theory (Dynamical Systems Theory)................................................................................ 29 2.3.3 Nonlinear Dynamics ..................................................................................................................... 33 2.4 PATTERN FORMATION FAR-FROM-EQUILIBRIUM & SELF-ORGANISATION......................................... 34 2.4.1 Pattern Formation Far-From-Equilibrium.................................................................................. 34 2.4.2 Self-Organisation.......................................................................................................................... 39 2.5 SELF-ORGANISED CRITICALITY ........................................................................................................... 45 3 METAL MINERAL DEPOSITS MODELS............................................................................................ 53 3.1.1 An Historical Sketch of the Genesis Models of Mineral Deposits............................................... 53 3.1.2 Metal Mineral Deposit Modelling................................................................................................ 60 3.1.2.1 Descriptive Models versus Genetic Models ......................................................................................... 62 3.1.2.2 Mineral Deposit Density Models.......................................................................................................... 67 3.1.2.3 Spatial-Temporal Models...................................................................................................................... 68 3.1.2.4 Structural Models.................................................................................................................................. 69 3.1.2.5 Statistical/Probabilistic Models............................................................................................................. 70 3.1.2.6
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