Multicomponent elemental and isotopic mixing in Ni-Cu-(PGE) ores at Kambalda, Western Australia

Most magmatic Ni-Cu-(PGE) deposits are considered to have formed from sulfi de-undersaturated silicate magmas and to contain a significant component of crustal sulfur that was derived via wholesale melting, partial melting, or devolatilization of wall rocks. Under such circumstances, the system may c omprise a silicate magma and a sulfide magma, with or without crystalline s olids, undissolved wallrock-derived xenoliths, an unmixed silicate xenomelt , or an undissolved xenovolatile phase, each of which may contain distinct chalcophile and lithophile components. Because traditional two-component (s ilicate: magma - sulfide magma) mass-balance models do not accurately model such systems, we have developed a series of multicomponent elemental and i sotopic mass-balance equations to model batch equilibration in magmatic Ni- Cu-(PGE) systems. We have applied them to the type examples of komatiite-as sociated Ni-Cu-(PGE) deposits at Kambalda, Western Australia. The calculati ons indicate that the elemental and isotopic compositions of the various co mponents in a multicomponent system will vary considerably as a function of the relative abundances of the components, and that different metals and i sotopic systems may decouple from each other, yielding apparently conflicti ng information regarding the sources of the components. The results suggest that the S isotopic and Zn compositions of the ores are more sensitive ind icators of contamination than the Os isotopes, and support a sediment-melti ng model for Kambalda.