Variations of Major and Minor Elements in Pt–Fe Alloy Minerals: A Review and New Observations

摘要: Compositional variations of major and minor elements were examined in Pt–Fe alloys from various geological settings types deposits, both lode placer occurrences. They included representatives layered intrusions, Alaskan-Uralian-(Aldan)-type alkaline gabbroic complexes, ophiolitic chromitites, numerous placers Canada, USA, Russia, other localities worldwide. alloy grains detrital occurrences are notably larger size, these considered to be the result a special conditions during crystallization such as temperature, pressure, geochemistry or time. In addition, number available statistical observations is much greater for occurrences, since they represent end-product of, some cases, weathering many millions tonnes sparsely mineralized bedrock. Typically, platinum-group (PGE) present admixtures (Ir, Rh, Pd) Cu, Ni incorporated into compositional series (Pt, PGE)2–3(Fe, Ni) Relative Cu enrichment poor Pt implies relatively fractionated melts at lower temperature. contrast distribution Ir, Pd fairly chaotic grains. There no relationship between levels with ratio Σ(Pt + PGE):(Fe Ni). The not common occurrences; nevertheless, show their maximums members this Global-scale datasets yield bimodal pattern diagram, which likely reflection miscibility gap ordered Pt3Fe structure (isoferroplatinum) disordered native ferroan platinum. plot versus Fe, there linear boundary due ideal ↔ Fe substitution. Two solid solution based on Ir-for-Pt Pd-for-Pt substitutions. incorporation Ir restricted Pt3Fe–Ir3Fe substitution (isoferroplatinum chengdeite, plus modifications). Besides, Ir0 appears replace Pt0 variants (Pt–Ir)–Fe alloys. good potential discovery new species Pd-dominant composition, (Pd, Pt)3Fe, most association mafic-ultramafic mafic units intrusions. “field complicated substitutions” recognized crystallochemical differences extending along Ir-Pd axis Ir–Pd–Rh diagram. inferred extends approximately line Ir–(Pd:Rh = 2:3). Minor presumably enters via coupled combination Rh. An Ir-enrichment trend typically occurs Alaskan-type complexes. large size nuggets associated complexes related an ultramafic-mafic pegmatite facies, whereas significant Pd-enrichment characteristic source-rocks (e.g., Coldwell Complex), resulting markedly different (wt.%). However, our examination dataset origins, we conclude that exhibit overlaps too useful reliable index-minerals.