Genetic Model
The genetic model of Kambalda-type Ni-Cu-(PGE) ore deposits is similar that of many other magmatic Ni-Cu-PGE ore deposits:
- Metal Source: komatiitic magma, which has been generated by high-degree partial melting of the mantle and which was strongly undersaturated in sulfide in the source (Wendland, 1982; see also Mavrogenes and O'Neill, 1999)
- Sulfur Source: S-rich country rocks (sulfidic sediments and volcanic rocks), from which the sulfide is melted by the high-temperature komatiite magma
- Dynamic System: Ni-Cu-Co-PGE are chalcophile and will preferentially partition from the silicate melt into the sulfide melt. The metal tenors (abundances in 100% sulfide) are enhanced by the flushing of voluminous komatiitic melt across the sulfide accumulation.
- Physical Trap: depressions in the footwall rocks, which may represent volcanic topographic irregularities modified by thermomechanical erosion. Sulfides within the komatiite lava flows are denser than the silicate melt and tend to pool within topographic lows, which may be enhanced in the lava channel by proposed thermal erosion of the substrate by the komatiite lava.
Recent research on the S isotopic compositions of komatiitic sulfides (Bekker et al., 2009) indicates that they lack the non-mass dependent isotope fractionation typical of sulfides formed at the surface during the Archaean, as would be expected if much of the sulfur was sourced from the sedimentary substrate, confirming that the S was derived 'upstream' in the system, not from the local country rocks.
Read more about this topic: Kambalda Type Komatiitic Nickel Ore Deposits
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