Continental Flood Basalts and Ore-Forming Processes

  • Sulfide Liquid Immiscibility: Two main types associated with ore formation:

    • Silicate-sulphide (Ni-Cu-PGE deposits)

    • Silicate-oxide (Fe-Ti-V-P deposits)

  • Silicate-Sulphide Immiscibility:

    • Documented as an ore-forming process.

    • Crucial in layered intrusions and flood basalts.

    • Key steps in formation:

    1. Sulphur saturation

    2. Equilibration with silicate magma

    3. Accumulation into layers

  • Sulphide Solubility: Influenced by temperature, FeO content (increases solubility), pressure, and SiO2 content (decreases solubility).

    • Maximum of 0.4extwt.%S0.4 ext{ wt.}\% S can dissolve at low crystallization.

  • Magma Evolution: Changes in sulphur saturation during fractionation are vital.

    • Example: Starting magma with 0.3extwt.%S0.3 ext{ wt.}\% S becomes saturated after fractionation.

  • Factors Promoting Immiscibility:

    • Early sulphur saturation: magma mixing, contamination by SiO2-rich and S-rich materials.

    • Late sulphide formation is detrimental.

  • Continental Flood Basalts (CFBs): Characterized by large flows and traps, distinguishable from oceanic plateaus.

    • Notable examples: Deccan Traps, Siberian Traps.

  • Large Igneous Provinces (LIPs): Rapid formation and extensive coverage within geological timeframes.

  • Mass Extinction Events: Associated with CFB eruptions:

    • E.g., Siberian Traps linked to the Permian-Triassic extinction event.

  • Notable Deposits: Norils’k-Talnakh deposit related to sulphide-rich magmas in Siberia; contains significant Ni-Cu-PGE and linked to extinction events.