Introduction to Geology PDF

INTRODUCTION Why Geology Economically Important Metal Concentrations in Earth’s Crust Concentration Metal (% by weight) Aluminum 8.0 Note for comparison: Iron 5.8 Silicon 28% Copper 0.0058 Oxygen 46% Nickel 0.0072 Zinc...

INTRODUCTION Why Geology Economically Important Metal Concentrations in Earth’s Crust Concentration Metal (% by weight) Aluminum 8.0 Note for comparison: Iron 5.8 Silicon 28% Copper 0.0058 Oxygen 46% Nickel 0.0072 Zinc 0.0082 Uranium 0.00016 Lead 0.001 Silver 0.000008 Gold 0.0000002  What is an ore deposit? An occurrence of minerals or metals in sufficiently high concentration to be profitable to mine and process using current technology and under current economic conditions.  What is ore grade? Ore grade is the concentration of economic mineral or metal in an ore deposit. · Weight percentage (base metals); iron, nickel, lead and zinc, copper. · Grams/tonne or oz/ton (precious metals) Gold, silver, platinum, and palladium.  Economically Important Metals Typical Grades of Ore Deposits Concentration Typical Grade Metal (% by weight) Metal (% by weight) Aluminum 8.0 Aluminum 30 Iron 5.8 Iron 53 Copper 0.0058 Copper 0.5-4 Nickel 0.0072 Nickel 1 Zinc 0.0082 Zinc 4 Uranium 0.00016 Uranium 0.3 Lead 0.001 Lead 5 Silver 0.000008 Silver 0.01 Gold 0.0000002 Gold 0.0001-0.001 Crustal Concentration What does it take to be an ore deposit? 2 10 Iron Aluminum 1 10 Lead Zinc Typical Orebody Concentration Copper 0 10 Nickel Uranium -1 y=x 10 -2 10 Silver -3 10 Gold -4 10 -7 -5 -3 -1 1 3 10 10 10 10 10 10 Crustal Concentration Crystal Settling in Cooling Magma  Hydrothermal Ore Deposits As magma cools, more abundant metals (silicon, aluminum) deposit first Solidification of magma releases water - a hydrothermal solution Minerals precipitate from hydrothermal solution and deposit in cracks or veins in rock Hydrothermal Fluids Hydrothermal Fluids Associated with Contact Metamorphism Hydrothermal Fluids Associated With Cooling Magmas Hydrothermal Fluids Associated With Subduction Zones Hydrothermal Fluids Associated With Subduction Zones  Sedimentary Ore Deposits Deposition of dense, resistant minerals in streams, lakes etc (Alluvial Deposits), e.g. Placer gold Precipitation of minerals from lakes-oceans (Evaporite Deposits), e.g. Potash and Salt Deposits Accumulation, burial and petrification of vegetation, e.g. Coal Deposits.  Banded Iron Formation (BIF) alternating bands of chert and iron minerals Fe precipitated from sea water in shallow basins The majority of are ~2.5 billion years and mark the beginning of oxygenated atmosphere on Earth  Metamorphic Ore Deposits Concentration of minerals caused by high temperatures and pressures near intrusions Examples: Lead-zinc deposits in southeast B.C. Diamonds Garnets Hydrothermal and Metamorphic Ore Deposits Geyser or hot spring Hydrothermal solutions entering veins in rocks Ore deposit zoning Alteration of rocks by heat and pressure Intrusion  Exploration Methods · Remote sensing · Geological mapping · Geophysical surveys · Geochemical surveys · Bulk sampling · Drilling (core or destructive) Airborne Geophysics Helicopter Bush Cable “Bird” See the video on Airborne Geophysics technique for mineral exploration: https://www.youtube.com/watch?v=CeQ7p2 NdkPc GEOPHYSICAL METHODS Geochemical Anomalies https://www.goldensoftware.com/success-stories/geochemical-mapping-of-urban- and-suburban-areas  Mineralogy determines recoverability Ore Gangue  Beneficiation Any process that improves (benefits) the economic value of the ore by removing the gangue minerals, which results in a higher grade product (concentrate) and a waste stream (tailings). Separation Techniques take advantage of the differences in characteristics between minerals: – Flotation: Attachment of minerals to air bubbles - hydrophibicity – Magnetic Separation: Apply magnetic field – Gravity Separation: differences in specific gravity of materials – Electrostatic Separation: Apply electrostatic polarity Particle size distribution has large influence on results