Kambalda type komatiitic nickel ore deposits

Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano.

The classification of the type of ore environment sets these apart from other magmatic Ni-Cu-PGE ore deposits, which share many of the same genetic (formational) controls.

Kambalda-type ore deposits are distinctive in that the deposition of an immiscible Fe-Ni-Cu sulfide melt occurs within a lava flow channel upon the palaeosurface. This is distinct from other magmatic Ni-Cu-PGE deposits, where Fe-Ni-Cu sulfide melt accumulates within a subvolcanic feeder dike, sill, or magma chamber.

The genetic model of Kambalda-type Ni-Cu-(PGE) ore deposits is similar that of many other magmatic Ni-Cu-PGE ore deposits:

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.

Komatiite-associated Ni-Cu-PGE deposits can form in a wide range of volcanic environments and overlie a wide range of footwall rocks, including basalts (e.g., Kambalda, Western Australia), andesites (e.g., Alexo, Ontario), dacites (e.g., Bannockburn, Ontario; Silver Swan, Western Australia), rhyolites (e.g., Dee's Flow, Ontario), sulfide facies iron-formations (e.g., Windarra, Western Australia), and sulfidic semi-pelites (e.g., Raglan, Quebec).

The morphology of Kambalda-type Ni-Cu-PGE deposits is distinctive because the Fe-Ni-Cu sulfides occur along the floor of a komatiite lava flow, concentrated within a zone of highest flow in the lava channel facies (Lesher et al., 1984).

The lava channel is typically recognised within a komatiite sequence by;

The ore zone typically consists, from the base upwards, of a zone of massive sulfides, matrix/net-textured sulfides, disseminated sulfides, and cloud sulfides.

Massive sulfides are not always present but where present are composed of >90% Fe-Ni-Cu sulfides occasionally with exotic enclaves of olivine, metasedimentary or melted material derived from the footwall to the lava flow. The massive sulfide normally sits upon a footwall of basalt or felsic volcanic rock, into which the massive sulfide may locally intrude, forming veins, interpillow sulfides, and interbreccia sulfides. Semi-massive sulfides are more common and are composed of 75-90% Fe-Ni-Cu sulfides with inclusions of olivine and wall rocks.

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