The platinum-group element geochemistry of chromitites and silicate rocks from Swat, northwestern Pakistan
Abstract
The concentrations of the Platinum-group elements (PGE) and Au were determined in a limited number of samples which represent chromitites, altered ultramafic and mafic rocks of the Swat valley ophiolite. The PGE characteristics of the chromitites mostly conform to the trend exhibited by the podiform chromitites. However, being sulphide-poor and containing Cr-rich chromite, the Pd content of one of the samples is anomalously high compared to similar chromitites from other areas. This enrichment in Pd is probably caused by a localized hydrothermal activity. The Ir content of the chromite-poor, altered ultramafic rocks is remark- ably uniform (4 ppb) and close to the values in mantle materials but their Pd (10 ± 3.7 ppb) and Au (5 ± 3.5 ppb) abundances are distinctly higher than the latter. These features of PGE and Au concentration of the host ultramafic rocks are consistent with an origin involving partial melting followed by hydrothermal alteration.
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