Ore Deposits 101: Lecture on Layer Complexes and Kimberlites

Lecture Overview

• Focus: Layer complexes and kimberlites
• Divided into two parts:
  1. Ore deposits in mafic-ultramafic complexes: Copper-nickel, massive sulfides, chrome, platinum group elements (PGEs)
  2. Diamonds in kimberlite intrusions

Key Concepts

• Mining limitations: Metals and minerals are mined from Earth's crust
• Concentration required for economic mining
• Partial melting of rocks to concentrate metals
• Mafic rocks: Rich in silica, sodium, potassium form light minerals (e.g., quartz, feldspar)
• Ultramafic rocks: Rich in iron, magnesium form dark minerals
• Mafic and ultramafic magmas crystallize at higher temperatures

Ore Deposits

Copper-Nickel Massive Sulfide Deposits

• Formation: Magma rich in copper and nickel, assimilates sulfur
• Examples:
  • Sudbury, Ontario: Meteorite impact theory
  • Noril'sk, Russia: Siberian traps, massive sulfides
  • Voisey's Bay, Labrador: Discovered by prospectors, valuable deposit
• Exploration Methods:
  • Magnetic surveys for intrusions
  • Electromagnetics and gravity surveys

Platinum Group Elements (PGE) and Chrome Deposits

• Formation in discrete layers in magma chambers
• Important components: Platinum, palladium, rhodium, chrome
• Examples:
  • Bushveld Complex, South Africa: Largest PGE resource
  • Stillwater Complex, Montana: Palladium-rich
  • Great Dyke, Zimbabwe: Long narrow outcrop
• Exploration Methods:
  • Initial magnetic survey
  • Geochemistry for critical horizons

Kimberlites and Diamonds

• Diamonds originate in kimberlite pipes
• Kimberlite: Ultramafic, derived from mantle
• Diamond formation: Requires specific conditions under continental plates
• Major producers: Sub-Saharan Africa, Russia
• Exploration Methods:
  • Magnetic and gravity surveys
  • Sampling for kimberlite indicator minerals (KIMs)

Key Takeaways

• Copper-nickel massive sulfides and PGEs/chrome deposits require large mafic intrusions
• Exploration methods differ for sulfide versus PGE/chrome deposits
• Diamonds originate in mantle and are carried by kimberlite magmas
• Economic diamond deposits are rare, located in specific geological settings

Next Lecture

• Focus on porphyry and iron oxide copper gold (IOCG) deposits