Gersdorffite types in the depositional sequence of the five-element ores in the Bihor metallogenic district, Apuseni Mountains: their compositional array and Raman identification of the gersdorffite polymorphs

The five-element mineralization of the Bihor metallogenetic district, Apuseni Mts., Romania contains three identifiable depositional stages, recording Co-fluctuations during a continuous increase of sulfur activity. Gersdorffite forming several chemical clusters precipitates overprinting a diarsenide-rich stage, later growing abundantly as krutovite-gersdorffite with nickeline, and replacing at different extents earlier assemblages. A Raman investigation on gersdorffites and accompanying phases revealed distinctive spectra. The compositional clusters of gersdorffite correlate with the Raman response, allowing the separation of near-stoichiometric gersdorffite, As-rich paragersdorffite and Co-Ni – substituted paragersdorffite.