💎Mineralogy Unit 15 – Economic Mineralogy and Mineral Resources

Key Concepts and Definitions

• Economic minerals valuable natural resources extracted from the Earth for commercial purposes
• Ore deposit concentration of one or more minerals that can be mined profitably
• Grade concentration of a valuable mineral within an ore deposit, typically expressed as a percentage or grams per tonne
• Cut-off grade minimum concentration of a valuable mineral that can be mined economically
• Reserves portion of an ore deposit that can be economically extracted using current technology and under present economic conditions
  • Proven reserves highest level of confidence based on extensive sampling and analysis
  • Probable reserves lower level of confidence based on less extensive sampling and analysis
• Resources portion of an ore deposit that has the potential to be economically extracted in the future, but may not be feasible under current conditions
• Gangue non-valuable minerals associated with the ore that must be separated during processing

Mineral Formation and Occurrence

• Magmatic deposits form from the crystallization of magma, often containing valuable metals (copper, nickel, platinum group elements)
  • Layered intrusions (Bushveld Complex, South Africa) form through fractional crystallization and settling of dense minerals
  • Pegmatites (Greenbushes, Australia) form from the crystallization of residual magma enriched in rare elements (lithium, tantalum, cesium)
• Hydrothermal deposits form from the circulation of hot, mineral-rich fluids through rocks, precipitating minerals in veins or disseminated throughout the host rock
  • Porphyry deposits (Chuquicamata, Chile) form from the intrusion of magma into the upper crust, creating large, low-grade deposits of copper and molybdenum
  • Epithermal deposits (Yanacocha, Peru) form at shallow depths and low temperatures, often containing gold and silver
• Sedimentary deposits form through the accumulation and concentration of minerals in sedimentary environments
  • Placer deposits (Witwatersrand Basin, South Africa) form from the mechanical concentration of heavy minerals (gold, platinum, diamonds) in river or beach sediments
  • Evaporite deposits (Salar de Atacama, Chile) form from the evaporation of mineral-rich waters in arid environments, producing deposits of lithium, boron, and potassium
• Metamorphic deposits form through the transformation of pre-existing rocks and minerals under high temperature and pressure conditions
  • Banded iron formations (Pilbara Craton, Australia) form from the metamorphism of sedimentary iron deposits, creating large, high-grade sources of iron ore
• Weathering and supergene enrichment processes can concentrate minerals near the Earth's surface through the action of water, oxygen, and other agents
  • Bauxite deposits (Weipa, Australia) form from the weathering of aluminum-rich rocks in tropical environments
  • Supergene enrichment (Chuquicamata, Chile) occurs when weathering processes concentrate valuable minerals (copper) near the surface, creating high-grade zones above the primary ore body

Classification of Economic Minerals

• Metallic minerals sources of valuable metals, typically extracted through mining and processing
  • Base metals (copper, lead, zinc, nickel) used in a wide range of industrial and consumer applications
  • Precious metals (gold, silver, platinum group elements) used in jewelry, investment, and industrial applications
  • Ferrous metals (iron, manganese, chromium) used primarily in the production of steel and other alloys
• Non-metallic minerals valuable for their physical and chemical properties, often used in industrial and construction applications
  • Industrial minerals (limestone, gypsum, salt, sulfur) used in the production of cement, plaster, chemicals, and other products
  • Fertilizer minerals (phosphate rock, potash) used in the production of agricultural fertilizers
  • Gemstones (diamonds, rubies, sapphires) valued for their beauty and used in jewelry and decorative objects
• Energy minerals fossil fuels and uranium used for power generation and transportation
  • Coal formed from the accumulation and compression of plant material over millions of years
  • Oil and gas formed from the burial and heating of organic matter in sedimentary basins
  • Uranium used as a fuel in nuclear power plants, typically extracted from sandstone or unconformity-related deposits

Exploration Techniques

• Geological mapping involves the identification and interpretation of rock units, structures, and mineralization patterns to guide exploration efforts
  • Field observations and measurements used to create detailed maps and cross-sections of the area of interest
  • Remote sensing techniques (satellite imagery, aerial photography) provide regional-scale information and help identify potential targets
• Geochemical surveys measure the concentration of specific elements in rock, soil, or water samples to identify anomalies that may indicate the presence of mineralization
  • Stream sediment sampling used to identify drainage basins with elevated concentrations of target elements
  • Soil sampling used to delineate the extent and grade of near-surface mineralization
  • Rock chip sampling used to assess the grade and distribution of mineralization in outcrops or drill core
• Geophysical surveys measure the physical properties of rocks and minerals to identify subsurface features and potential ore bodies
  • Magnetic surveys detect variations in the Earth's magnetic field caused by the presence of magnetic minerals (magnetite)
  • Gravity surveys measure variations in the Earth's gravitational field caused by differences in rock density
  • Electromagnetic surveys measure the electrical conductivity of rocks and can identify conductive minerals (sulfides) associated with mineralization
• Drilling used to obtain subsurface samples and provide detailed information on the grade, thickness, and continuity of mineralization
  • Diamond drilling uses a rotary drill with a diamond-impregnated bit to recover a continuous core sample
  • Reverse circulation drilling uses a pneumatic hammer to produce rock chips that are collected at the surface
  • Drilling results used to create 3D models of the ore body and estimate mineral resources and reserves

Mining and Extraction Methods

• Surface mining methods used when the ore body is relatively close to the surface and can be accessed by removing the overlying rock and soil
  • Open-pit mining involves the creation of a large, stepped excavation to extract the ore, commonly used for low-grade, disseminated deposits (copper porphyries)
  • Strip mining involves the removal of overburden in long, narrow strips to access shallow, tabular ore bodies (coal seams)
  • Placer mining involves the excavation and processing of unconsolidated sediments to recover heavy minerals (gold, diamonds)
• Underground mining methods used when the ore body is deep or has a high grade, making surface mining uneconomical
  • Room-and-pillar mining involves the creation of a network of rooms and pillars to extract the ore, leaving some material in place for support (coal, salt)
  • Cut-and-fill mining involves the extraction of ore in horizontal slices, with waste rock or cement used to fill the void and provide a working platform for the next slice
  • Block caving involves the undercutting of a large ore body, allowing it to collapse under its own weight into draw points for extraction (copper, molybdenum)
• Mineral processing involves the separation of valuable minerals from the gangue material using physical, chemical, or biological methods
  • Comminution involves the crushing and grinding of the ore to liberate the valuable minerals from the gangue
  • Concentration involves the separation of the valuable minerals from the gangue using methods such as flotation, gravity separation, or magnetic separation
  • Hydrometallurgy involves the extraction of metals from the concentrate using aqueous solutions, such as leaching, solvent extraction, and electrowinning
  • Pyrometallurgy involves the extraction of metals from the concentrate using high-temperature processes, such as smelting and refining

Economic and Market Factors

• Supply and demand dynamics influence the price and profitability of mineral commodities
  • Global economic growth and industrialization drive demand for base metals (copper, aluminum) and energy minerals (coal, oil)
  • Technological advancements and changing consumer preferences can create new markets for specific minerals (lithium for batteries, rare earth elements for electronics)
  • Geopolitical events and trade policies can disrupt supply chains and affect prices (conflict in mineral-rich regions, tariffs on imported goods)
• Production costs determine the economic viability of a mining project and are influenced by factors such as the grade and size of the ore body, the mining and processing methods, and the location and infrastructure
  • Capital costs include the initial investment in mine development, equipment, and infrastructure
  • Operating costs include the ongoing expenses associated with mining, processing, and transportation
  • Cut-off grade is determined by the balance between production costs and the market price of the commodity
• Financing and investment are critical for the development of mining projects, which often require significant upfront capital
  • Equity financing involves the sale of ownership shares in the mining company to raise funds
  • Debt financing involves borrowing money from banks or other lenders to fund the project
  • Joint ventures and partnerships allow companies to share the risks and costs of a project while leveraging each other's expertise and resources
• Commodity markets and price fluctuations can have a significant impact on the profitability and viability of mining projects
  • Spot prices reflect the current market value of a commodity and can be volatile in response to short-term supply and demand factors
  • Future contracts allow buyers and sellers to agree on a price for the delivery of a commodity at a specific date in the future, providing some price stability and hedging opportunities
  • Commodity exchanges (London Metal Exchange, Chicago Mercantile Exchange) facilitate the trading of mineral commodities and provide price discovery and risk management tools

Environmental Considerations

• Land use and ecosystem impacts are major concerns associated with mining activities, as they can result in the destruction or alteration of natural habitats
  • Deforestation and land clearing can lead to the loss of biodiversity and ecosystem services
  • Erosion and sedimentation can affect water quality and aquatic habitats downstream of the mining site
  • Reclamation and rehabilitation practices aim to restore the land to a stable and productive state after mining is completed
• Water management is critical in mining operations, as large quantities of water are often required for processing and dust suppression, while mine drainage can impact water quality
  • Water efficiency and recycling practices can help reduce the overall water footprint of the mining operation
  • Acid mine drainage occurs when sulfide minerals are exposed to air and water, generating acidic runoff that can contaminate nearby water sources
  • Water treatment and monitoring systems are used to manage and mitigate the impacts of mine drainage on the environment
• Air quality and greenhouse gas emissions are important considerations in mining, as operations can generate significant amounts of dust, particulate matter, and other pollutants
  • Dust suppression techniques (water sprays, enclosures) are used to minimize the release of particulate matter from mining and processing activities
  • Greenhouse gas emissions from the burning of fossil fuels and the use of electricity contribute to climate change and are subject to increasing regulation and carbon pricing mechanisms
  • Energy efficiency and renewable energy initiatives can help reduce the carbon footprint of mining operations
• Waste management is a critical aspect of responsible mining, as large volumes of waste rock and tailings are generated during the extraction and processing of ore
  • Tailings dams are used to store the fine-grained waste material from mineral processing, but can pose significant risks if not properly designed and managed (Brumadinho dam disaster, Brazil)
  • Waste rock management involves the careful placement and contouring of non-ore material to minimize erosion and environmental impacts
  • Acid-generating waste requires special handling and storage to prevent the formation of acid mine drainage
• Social and community impacts of mining can be significant, as projects often take place in remote or developing regions with limited infrastructure and economic opportunities
  • Community engagement and consultation are essential for building trust and understanding between the mining company and local stakeholders
  • Social investment programs (education, healthcare, infrastructure) can help promote sustainable development and improve the quality of life in mining communities
  • Indigenous rights and cultural heritage must be respected and protected, with free, prior, and informed consent obtained before any mining activities take place on traditional lands

Case Studies and Applications

• Copper porphyry deposits (Escondida, Chile) are the world's primary source of copper, formed by the intrusion of magma into the upper crust
  • Large, low-grade deposits are mined using open-pit methods and processed using flotation to produce a copper concentrate
  • Responsible water management is critical in the arid Atacama Desert, with desalination and water recycling used to reduce the impact on local water resources
• Rare earth elements (Mountain Pass, USA) are critical for the production of high-tech products, including smartphones, wind turbines, and electric vehicles
  • Deposits are typically associated with alkaline igneous rocks and are mined using open-pit methods
  • Processing involves a complex series of steps, including flotation, roasting, and leaching, to separate the individual rare earth elements
  • China currently dominates the global supply of rare earth elements, raising concerns about supply security and geopolitical risks
• Lithium brine deposits (Salar de Atacama, Chile) are a key source of lithium for the growing battery industry, as demand for electric vehicles and energy storage increases
  • Lithium is extracted from salt brines in closed basins through a process of evaporation and chemical treatment
  • Environmental concerns include the impact on local water resources and fragile desert ecosystems
  • Social issues related to the rights and livelihoods of indigenous communities living near the salt flats have led to conflicts and legal challenges
• Conflict minerals (coltan, Democratic Republic of Congo) are those mined in areas of armed conflict and human rights abuses, with the proceeds often used to finance further violence
  • Coltan is a key source of tantalum, used in the production of electronic capacitors for smartphones and other devices
  • International efforts to promote supply chain transparency and due diligence aim to reduce the trade in conflict minerals and support responsible sourcing practices
  • Artisanal and small-scale mining of conflict minerals poses significant challenges, as it is difficult to regulate and often involves poor working conditions and environmental damage
• Diamonds (Jwaneng, Botswana) are an example of how responsible mining practices and good governance can contribute to sustainable development
  • Botswana has used its diamond wealth to invest in education, healthcare, and infrastructure, achieving significant reductions in poverty and improvements in social indicators
  • The country's partnership with De Beers has emphasized local employment, skills development, and value addition through diamond cutting and polishing
  • Kimberley Process Certification Scheme aims to prevent the trade in "blood diamonds" that finance armed conflicts, through a system of export and import controls