Publication Type:

Book Chapter


Geological Society of America, 2000 annual meeting, Geological Society of America (GSA), Boulder, CO, United States, Volume 32, p.4 (2000)




copper ores, cumulates, fluorine, fractional crystallization, halogens, host rocks, Immiscibility, mafic composition, magmas, melts, metal ores, nickel ores, partitioning, phase equilibria, platinum ores, properties, solubility, sulfides, sulfur, Temperature, ultramafic composition


Most magmatic Ni-Cu-(PGE) sulfide deposits are hosted by mafic-ultramafic cumulate rocks interpreted to represent dynamic lava channels or magma conduits that appear to have formed from magmas which incorporated variable amounts of crustal sulfur. Although we have a general understanding of the ore-forming processes and the tectonic and geological environments in which these deposits do and do not occur, there are several outstanding problems that will focus our research activities for the next decade: sulfide solubility, chalcophile element partitioning, and fluid dynamics. Although it has been shown that the solubility of sulfide in a sulfide-undersaturated magma increases with decreasing P and decreases with decreasing T, increasing fO2, increasing fS2, and increasing aSiO2, we do not know the precise geometry of the sulfide saturation surface as a function of these parameters and therefore do not have a clear understanding of the mechanisms by which magmas achieve sulfide saturation during ascent, emplacement, contamination, and crystallization or the amount of "magmatic" sulphide that can be extracted from a magma. Similarly, although we have a general understanding of the partitioning behavior of chalcophile elements (Co, Ni, Cu, PGEs) between silicate magmas and sulfide melts, we do not know precisely how the partition coefficients and ore compositions vary as a function of T, composition, fO2, and fS2. Finally, although we know that sulfide melts are very dense, very fluid, and remain molten at temperatures well below the solidus of most silicate melts, we do not understand the phase equilibria and fluid dynamic behavior of immiscible sulfide melts and the mechanisms by which they are fractionated and/or segregated to form economic ore deposits. Better knowledge of these processes, combined with improvements in geophysical methods/models and geochemical methods/models, will permit us to better predict which mafic and ultramafic rocks may host economic abundances of Ni-Cu-(PGE) mineralization, how ore tenor varies with changes in the intensive and extensive properties of the magmas, and where economic abundances of Ni-Cu-(PGE) sulfides may be localized.


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