Precious metals in the Jimberlana Intrusion, Western Australia; implications for the genesis of platiniferous ores in layered intrusions

A neutron activation study of the distribution of Ir, Pd, and An in the Jimberlana Intrusion has shown that Pd and Au partition strongly into the sulfides. The Pd content of sulfides is governed, to a large degree, by the R factor, a measure of the amount of silicate liquid in equilibrium with the sulfide melt. The Pd content of the sulfide horizons from the center of the Jimberlana Intrusion is high but appreciably less than that of the Merensky Reef and the Pt horizon of the Stillwater Complex. The comparatively low Pd content of the Jimberlana sulfides is believed to be due to the sulfides having reached equilibrium with a smaller volume of silicate liquid than the Pt-rich sulfides of the Bushveld and Stillwater Complexes.At the margin of Jimberlana the sulfide content of the rocks may be as high as 10 percent. These sulfides have precipitated rapidly, resulting in a very low R factor and consequently they have anomalously low precious metal contents.Variations in the Ir content of rocks are independent of the presence of sulfides in the Jimberlana Intrusion. This may have resulted from the f (sub O 2 ) of the magma being less than that of the Ir 2 S 3 /Ir buffer allowing Pd, but not Ir, to enter the sulfide melt.