Publication Type:
Book ChapterSource:
Geological Society of America, 1999 annual meeting, Geological Society of America (GSA), Boulder, CO, United States, Volume 31, p.22 (1999)ISBN:
0016-7592Keywords:
Asia, Australasia, australia, Commonwealth of Independent States, copper ores, Duluth Complex, emplacement, Europe, isotope ratios, Isotopes, Kambalda Australia, Krasnoyarsk Russian Federation, lava, magmas, metal ores, mineral composition, mineral deposits, genesis, Minnesota, nickel ores, Norilsk region, norway, platinum ores, Russian Federation, S-34/S-32, saturation, Scandinavia, Stable isotopes, sulfides, sulfur, Taymyr Dolgan-Nenets Russian Federation, Trace elements, United States, Western Australia, Western EuropeAbstract:
The concept of sulfide magmas originated at the turn of the century with studies of Norwegian deposits. As Sudbury became the world's principal source of Ni, in situ settling of sulfides from overlying magma dominated ideas about genesis. Recognition of Sudbury as an astrobleme raised questions as to the universal application of concepts derived from this area. Work at Kambalda showed the importance of sulfide concentration in lava channels. S-isotopic work on the Noril'sk and Duluth intrusions, coupled with the identification of thermal erosion at Kambalda highlighted external sulfur as a cause of sulfide immiscibility, as did the realisation that source magmas for all economic magmatic sulfide deposits must have been sulfide-unsaturated on leaving the mantle, and experimental data that showed that within themselves such magmas would not achieve sulfide saturation as they rose into the crust. Trace element and isotopic studies of host mafic/ultramafic bodies at Noril'sk, Sudbury, Duluth, Kambalda and Voisey's Bay and other localities showed crustal contamination to be have occurred. As experimental partition coefficients, coupled with data on the PGE content of ores, became available, the importance of the magma/sulfide ratio ("R" or "N" factor) in sulfide genesis was appreciated. In turn chalcophile depletion signatures (as determined from associated volcanics, or the Ni content of olivine and Cu/Zr ratios of cumulus rocks) became important in assessing igneous bodies as hosts for ores. Physical modelling of sulfide settling pointed to the need for processes other than gravitational settling to concentrate sulfides. This, along with the recognition that the Noril'sk, Voisey's Bay and most komatiite ores occur in magma conduits, has demonstrated the importance of hydrodynamic forces active during flow of mixtures of magma and sulfide. Each of these developments has, in turn, strongly influenced mineral exploration models. It is now appreciated that Ni-Cu-(PGE) deposits can form from a wide range of mafic/ultramafic magma types generated in diverse tectonic settings, and that the composition of the magma (and mantle source) is less important than the nature of the interactions with crustal rocks which have occurred during emplacement.
Notes:
GeoRef, Copyright 2018, American Geological Institute.<br/>2000-045154<br/>Voisey's Bay
