Raman spectra of synthetic ‘braggite’ ((Pd,Pt,Ni)S) vary systematically with changes in Pt/Pd ratios, but this change is less pronounced than in ‘cooperite’ ((Pt,Pd,Ni)S). Compared to ‘vysotskite’ (ideally PdS), the incorporation of Pt leads to broadening of bands but the spectra of ‘vysotskite’ and ‘braggite’ are similar, and spectra of ‘cooperite’ and the ‘braggite/vysotskite’ solid-solution series are sufficiently different to facilitate distinction of these platinum group minerals by Raman spectroscopy.

Platinum-group minerals (PGM) from placer deposits in Colombia, California, Oregon and Alaska were investigated with the electron microprobe, proton microprobe (μ-PIXE) and ion probe to analyse their major and trace element contents and 187Os/186Os isotopic ratios. Most of the grains in the samples investigated proved to be essentially homogeneous alloys of Pt-Fe and Os-Ir-Ru although a few of them contained inclusions of other PGM such as cooperite and laurite. Detailed analyses were undertaken on the Os-Ir-Ru alloy phases.

The 187Os/186Os isotope ratios fell into a range from 1.005 to 1.156 and are consistent with data published on PGM from other placer deposits from these regions. The ratios, together with the trace element data (and in particular the low rhenium content) determined by ion probe and μ-PIXE, indicate that crustal osmium was not incorporated in the grains and that no significant evolution of the 187Os/186Os ratios occurred during their history. These data, along with mineralogical and textural evidence, are consistent with a mantle origin for the grains through ultramafic intrusions, although the data do not entirely rule out alternative interpretations.

A reappraisal of Hermann's ‘irite’, described in 1836 and 1841, has been attempted by examining and analysing three museum samples, accessioned before 1865. The three samples were determined to be mixtures of chromite, native Os and Ir, rutheniridosmine, platinum, laurite, hongshiite, irarsite, cuprorhodsite, iridsite, prassoite, hollingworthite, erlichmannite, several Ru-Ir-Pt-Ti-Cr-Fe oxide/ hydroxide compounds (sometimes well crystallized), Pt-Ir-K chlorocompounds, and Pt-Ir-Ru-K-Clcontaining opal. The latter two are considered as artifacts generated by the hydrometallurgical processes applied to the crude platinum ores. Individual particles of native iridium and osmium display baroque crystal habits (filaments, leafs, blades, hollow crystals) that could be their natural, although rarely observed, states. There is still doubt about the origin (either natural or artificial) of all Ru-Ir-Pt- Ti-Cr-Fe oxides, but they can be compared with those found in several pristine placer and hard-rock deposits worldwide and in the Urals.