Lecture Notes on Ore Deposits 101: VMS and Sedex Deposits

Introduction

• Speaker: Andrew Jackson, Economic Geologist at Global Resource Investments
• Objective: Provide understanding of ore deposits for non-technical audiences
• Focus of Lecture: Volcanogenic Massive Sulfides (VMS) and Sedimentary Exhalative (Sedex) deposits

General Concepts

• Metal Concentration Process: Melting of crustal rocks, rise of melt through the crust, concentration of metals
• VMS and Sedex Deposits: Products of sea-floor smokers with different geological settings

Volcanogenic Massive Sulfides (VMS)

• Formation:
  • Occur at or near the sea floor
  • Copper and zinc-rich, associated with volcanic activity
  • Massive sulfide cap on the sea floor, with underlying "feeder" or "Stringer" zone
• Characteristics:
  • Often form in clusters over large heat sources
  • Found worldwide, significant in copper and zinc production
  • Common in geological history, still forming today
• Structure:
  • Consist of massive sulfide cap and underlying "Stringer Zone"
  • Funnel-shaped neck of fractured rock
  • Metal deposition influenced by rapid cooling
  • Spatially zoned metals: copper near vents, zinc and lead more distal
• Economic Importance:
  • Economically significant, particularly for Canada
  • Range in size from 4 to 25 million tons, with some exceptions
• Examples:
  • Bisha deposit in Eritrea and Solwara 1 deposit off Papua New Guinea

Sedimentary Exhalative (Sedex) Deposits

• Formation:
  • Not directly related to volcanic activity
  • Driven by dewatering and metamorphism of sediments
  • Lead, zinc, and silver dominant
• Characteristics:
  • Form in fault-bounded sedimentary basins
  • Generally larger and higher grade than VMS deposits
  • Fewer in number
• Economic Importance:
  • Major source of lead and zinc
  • Range from 1 million to 400 million tons
• Examples:
  • Sullivan deposit in British Columbia

Exploration Techniques

• Common Techniques:
  • Soil and rock geochemistry
  • Electromagnetic geophysics (EM)
  • Magnetics and gravity
• Exploration Strategy:
  • Identify time breaks in sedimentation
  • Focus on stratigraphic sequences and fault zones
  • Drill testing based on geophysical and geochemical data
• Example Program: Tarsis's YMD property exploration in Yukon

Key Takeaways

• Both VMS and Sedex are submarine hot spring deposits
• VMS: Volcanic-hosted, copper and zinc, common
• Sedex: Sediment-hosted, zinc and lead, less common but larger
• Exploration uses geophysics and geochemistry extensively
• Future potential for sea-floor mining with high-grade deposits

Conclusion

• Next lecture topic: V vant gold deposits of South Africa, a major source of gold

These notes provide an overview of the geological and economic aspects of VMS and Sedex deposits, key exploration techniques, and examples of significant deposits.