2026-04-19T11:35:23Zhttps://recercat.cat/oai/request

oai:recercat.cat:2445/1631222025-11-19T10:53:12Zcom_2072_1057col_2072_478917col_2072_478923

00925njm 22002777a 4500 dc Aiglsperger, Thomas Hans author Proenza Fernández, Joaquín Antonio author Font Bardia, Ma. Mercedes author Baurier Aymat, Sandra author Galí Medina, Salvador, 1949- author Lewis, J. F. author Longo, Francisco author 2020-05-29T14:12:13Z 2020-05-29T14:12:13Z 2017-02 2020-05-29T14:12:13Z Ni-laterites from the Dominican Republic host rare but extremely platinum-group element (PGE)-rich chromitites (up to 17.5 ppm) without economic significance. These chromitites occur either included in saprolite (beneath the Mg discontinuity) or as 'floating chromitites' within limonite (above the Mg discontinuity). Both chromitite types have similar iridium-group PGE (IPGE)-enriched chondrite normalized patterns; however, chromitites included in limonite show a pronounced positive Pt anomaly. Investigation of heavy mineral concentrates, obtained via hydroseparation techniques, led to the discovery of multistage PGE grains: (i) Os-Ru-Fe-(Ir) grains of porous appearance are overgrown by (ii) Ni-Fe-Ir and Ir-Fe-Ni-(Pt) phases which are overgrown by (iii) Pt-Ir-Fe-Ni mineral phases. Whereas Ir-dominated overgrowths prevail in chromitites from the saprolite, Pt-dominated overgrowths are observed within floating chromitites. The following formation model for multistage PGE grains is discussed: (i) hypogene platinum-group minerals (PGM) (e.g. laurite) are transformed to secondary PGM by desulphurization during serpentinization; (ii) at the stages of serpentinization and/or at the early stages of lateritization, Ir is mobilized and recrystallizes on porous surfaces of secondary PGM (serving as a natural catalyst) and (iii) at the late stages of lateritization, biogenic mediated neoformation (and accumulation) of Pt-Ir-Fe-Ni nanoparticles occurs. The evidence presented in this work demonstrates that in situ growth of Pt-Ir-Fe-Ni alloy nuggets of isometric symmetry is possible within Ni-laterites from the Dominican Republic. Nitrats Platí Minerals de platí República Dominicana Nitrates Platinum Platinum ores Dominican Republic Supergene neoformation of Pt-Ir-Fe-Ni alloys: multistage grains explains nugget formation in Ni-laterites