Applied Mineralogy Lecture 7b 2024 PDF

Minerals, Humankind and Me Week 7b: Mineral deposit and ore formation Applied Mineralogy for Chemical Engineers (GEO2006S) Prof Megan Becker Centre for Minerals Research, Dept Chemical Engineering September 2024 Mineral deposits ‘M...

Minerals, Humankind and Me Week 7b: Mineral deposit and ore formation Applied Mineralogy for Chemical Engineers (GEO2006S) Prof Megan Becker Centre for Minerals Research, Dept Chemical Engineering September 2024 Mineral deposits ‘Mineral deposits form when a useful commodity is sufficiently concentrated in an accessible part of the Earth’s crust so that it can be profitably extracted’ Robb (2005)  Mineral deposits Metallic ore deposits: mined and processed for the minerals containing valuable metals, e.g. Au, Pt, Cu, Pb, Zn, Ni. Non-metallic deposits: mined and processed for their physical properties or non-metallic element content e.g. salt, phosphate, gravels, dimension stone. Also known as industrial minerals. Energy: nuclear energy, fossil fuels (coal, oil, gas). None of the fossil fuels are minerals. Skinner (1990) Soutpan near Bloemfontein, Mail & Guardian Mineral resources and reserves Mineral resource: Concentration of mineral deposits of economic interest within the earth’s crust. To count as a mineral resource, these minerals must be in a form, grade, and quantity that is of economic interest for extraction. Mineral reserve: The portion of a mineral resource that can be realistically and economically mined. A mineral reserve must be proven by a detailed evaluation program, usually involving drilling and geophysical testing, to prove that a deposit is of sufficient quantity and quality to be defined as a viable, economically mineable reserve. The terminology of resources and reserves has legal implications and must be done by a registered ‘competent person’. Different countries have their own reporting standards. Mineral resources and reserves SAMCODE (2009)  Relative abundance of metals ‘Abundance (atom fraction) of the chemical elements in Earth's upper continental crust as a function of atomic number. The rarest elements in the crust (shown in yellow) are the most dense. They were further rarefied in the crust by being siderophile (iron-loving) elements, in the Goldschmidt classification of elements. Siderophiles were depleted by being relocated into the Earth's core. Their abundance in meteoroid materials is relatively higher. Additionally, tellurium and selenium have been depleted from the crust due to formation of volatile hydrides’. Relative associations of metals From the pioneering geochemist – Goldschmidt (1937) Lithophile – associated with silicates and concentrated in the crust Chalcophile – associated with sulfides Siderophile – occur as native metal and concentrated in the core Atmophile – occur as gas in the atmosphere Robb (2005) Relative associations of elements Relative associations of elements Robb (2005) Sustainability of mineral deposits Robb (2005) The critical metals list Metals that are critical based on economic importance and supply risk! Many of these are ‘geochemically scarce’.  The ‘mineralogical barrier’ Proposed by Skinner (1976). “A Second Iron Age Ahead? The distribution of chemical elements in the earth’s crust sets natural limits to man’s supply of metals that are much more important to the future of society than limits on energy” Considering geochemically abundant and geochemically scarce metals Concept of the mineralogical barrier can be extended beyond Skinner (1976) definition, to encompass other mineral-challenges where innovation is required (Becker et al. 2017) Geochemically scarce & abundant metals Skinner (1976) Geochemically scarce & abundant metals Innovative technology Skinner (1976) Sustainability of ore deposits For geochemically abundant metals: Metals comprise major elements in rock forming minerals with current mining operating for high grade ores. For geochemically scarce metals: Current mining of these metals as major elements in ore forming minerals (e.g. Cu in chalcopyrite). Lower grade ore deposits will comprise these metals substituting for major elements in rock forming minerals (e.g. substitution of Cu for Fe in mica), i.e. no discrete ore forming minerals exist. An inherent ‘mineralogical’ barrier exists between these two styles of mineralization. Technological innovation is key to unlocking the value of these low grade ores. The ‘mineralogical barrier’ is a useful concept that be applied across all aspects of mining and processing.  Some ore deposit terminology Ore: any naturally occurring material from which a mineral or aggregate of value can be extracted at a profit Syngenetic: ore deposits that form at the same time as their host rocks Epigenetic: ore deposits that form after their host rocks Hypogene: mineralization caused by ascending hydrothermal solutions Supergene: mineralization caused by descending solutions Epithermal: hydrothermal deposits formed at shallow depths (< 1500m) and fairly low temp (50-200ºC) Mesothermal: hydrothermal deposits formed at intermediate depths (1500- 4500 m) and temp (200-400 ºC) Hydrothermal: hydrothermal deposits formed at substantial depths (> 4500m) and elevated temp (400-600ºC) Placer: A deposit of sand or gravel in the bed of a river, lake or beach containing particles of valuable minerals Robb (2005) A simple ore classification Robb (2005) More complex ore classification Composition of the deposit Form of the deposit (size, shape, orientation and ore mineral distribution) Associated host rocks or geological structures (ore associations) Interpreted genesis of the deposit (processes, controls) McQueen (2005) Even more complex ore classification McQueen (2005) Formation of ore deposits ‘Four basic requirements for ore deposit formation: (i) A source for the ore components (metals and ligands) (ii) A mechanism that either transports these components to the ore deposit site and allows the appropriate concentration or removes non-ore components to allow residual concentration (iii) A depositional mechanism (trap) to fix the components in the ore body as minerals and associated gangue (iv) A process or geological setting that allow the ore deposit to be preserved.’ McQueen (2005) Formation of ore deposits McQueen (2005) Recap Moment Resource vs reserves (