PLATINUM-GROUP MINERALS FROM THE SANTIAGO RIVER, ESMERALDAS PROVINCE,ECUADOR

The first platinum-group minerals (PGM) to be described in detail from Ecuador come from placers in the Santiago River. Esmeraldas Province. This area is situated between the Cordillera de Toisan and the Pacifi c coast in the northwestern part of the country. The only PGM found as individual mineral grains in the placers are Pt-Fe alloys, mainly nat ive platinum with minor isoferroplatinum. Minerals found as inclusions in Pt-Fe alloys are hongshiite, osmium, bowieite, cuprorhodsite, laur ite, erlichmanite, cooperite, braggite, unknown phases in the systems Pd-As-Te, Pd-Cu-S and Pt-Cu-S, and chalcopyrite. The PGM in the placer s are inferred to derive from a mafic-ultramafic Alaskan-type intrusio n that has yet to be identified.