The ultramafic-mafic complex at W district, China, is composed of clinopyroxenite, hornblendite, gabbro and a variety of vein rocks. Three facies can be recognized in the clinopyroxenite body, i.e., the olivine-clinopyroxenite (lower part), diopsidite (the intermediate part) and the hornblende clinopyroxenite (the upper part)facies. In general, the concentration of palladium and platinum decreases with increasing silica content of the rocks. In the clinopyroxenite body the two elements are enriched in the diopsidite facies, which has the highest Mg/Fe ratio. Palladium and platinum contents of the vein rocks are comparable to that of their host rocks,auggesting a possible extraction of these metals from the latter. Palladium and platinum are present mainly as individual minerals in rocks and ore bodies and occur only in small amounts in sulfides as isomorphous impurities.Among the mineral phase, platinum occurs mostly as arsenide, while tellride, and particularly anthnonide, or any combination of bismuthide, telluride, and antimomde,are the principal mode of occurrence of palladium. All of these minerals are found intimately intergrown with pyrrhotite. In the magmatie stage, differentiation of palladium and platinum took place, accompanied by an increase in Pd/Pt ratio with increasing rock acidity in the complex.Pd/Pt ratios of vein rocks are higher than that of host rocks injected by them,indicating that decreasing temperature may be more favorable.for palladium enrich-ment than platinum. Within the mineralized zone, Pd/Pt ratio increases from foot wall to hanging wail and, within the ore body, is characterized by a distribution pattern which displays a higher value in the center and lowers down towards both ends laterally and vertically. It is thus clear from these observations that palladium is much more mobile at elevated temperatures and significant precipitaion can only be expected during cooling. Under supergene conditions, palladium is more active than platinum, leading to a decrease in Pd/Pt ratio. Palladium and platinum are closely associated with each other in hypogene and supergene zones, exibiting a marked positive correlation. In hypogene zone, palladium and platinum show no correlation with nickel, while a negative correlation with copper and cobalt and a positive correlation with tellurium and arsenic are readily evident. In supergene zone, the two elements bear no apparent relation to copper and nickel within leaching zones where sedimentation is evidenced, but demonstrate a negative correlation with copper, nickel and cobalt where leaching alone has developed. In this district, tellurium, arsenic, antimony and bismuth can be used as direct indicators for palladium and platinum; whereas sulfide zone can still serve as useful indications for palladium aad platinum enricbment, although the two elements show no strong correlation with copper, nickel and cobalt.
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