Most komatiite-associated magmatic Ni-Cu-(PGE) sulfide deposits formed from
sulfide-undersaturated magmas and are interpreted to have formed in dynami
c lava channels or magma conduits by incorporation of crustal sulfur. They
commonly exhibit geochemical and isotopic evidence of crustal contamination
and chalcophile element depletion on the scale of individual cooling units
or parts of individual cooling units that appear to be associated with the
err-forming process. It is possible, therefore, to discriminate between ro
cks generated during ore-forming processes and rocks generated during norma
l igneous processes by identifying signatures characteristic of crustal con
tamination (e.g., Th-U-LREE enrichment, negative Nb-Ta-Ti anomalies) or sul
fide segregation (e.g., Co-Ni-Cu-PGE depletion) (or both) and distinguishin
g them from signatures characteristic of normal igneous fractionation or ac
cumulation of crystals. The amounts of contamination and chalcophile elemen
t depletion produced during the ore-forming process depend on several facto
rs: 1) the stratigraphic architecture of the system (e.g., thickness and ph
ysical accessibility of the contaminant), 2) the fluid dynamics and thermod
ynamics of the lava or magma, 3) the physical, chemical, and thermal charac
teristics of the contaminant, 4) the amount of contaminant melted and incor
porated (e.g., amount of silicate partial melt), 5) the sulfur and metal co
ntent of the contaminant, 6) the initial saturation-state of sulfide in the
magma, 7) the assimilation:crystallization ratio, 8) the amount of lava re
plenishment, and 9) the effective magma:sulfide ratio (R factor) of the sys
tem. Because these processes vary independently from deposit to deposit, fr
om area to area within a deposit, and within a single area with time, there
are many opportunities to decouple contamination from chalcophile element
depletion.