Platiniferous Tetra-Auricupride: A Case Study from the Bolshoy Khailyk Placer Deposit, Western Sayans, Russia

Abstract

Tetra-auricupride, ideally AuCu, represents the only species showing the coexistence of Au with an elevated level of Pt, as in the case of a detrital grain studied structurally for the first time, from an ophiolite-associated placer at Bolshoy Khailyk, western Sayans, Russia. We infer that tetra-auricupride can incorporate as much as ~30 mol. % of a “PtCu” component, apparently without significant modification of the unit cell. The unit-cell parameters of platiniferous tetra-auricupride are: a 2.790(1) Å, c 3.641(4) Å, with c/a = 1.305, which are close to those reported for ordered AuCu(I) in the system Au–Cu, and close also to the cell parameters of tetraferroplatinum (PtFe), which both appear to crystallize in the same space group, P4/mmm. These intermetallic compounds and natural alloys are thus isostructural. The closeness of their structures presumably allows Pt to replace Au atoms so readily. The high extent of Cu + Au enrichment is considered to be a reflection of geochemical evolution and buildup in levels of the incompatible Cu and Au with subordinate Pt in a remaining volume of melt at low levels of fO2 and fS2 in the system.

Editorial for the Special Issue “Platinum-Group Minerals: New Results and Advances in PGE Mineralogy in Various Ni-Cu-Cr-PGE Ore Systems”

“…The occurrence of a rare Pt-enriched tetra-auricupride was documented by Barkov et al [11] from an ophiolite-associated placer at Bolshoy Khailyk, western Sayans, Russia. The authors, based on the chemical composition and a synchrotron micro-Laue diffraction study, concluded that tetra-auricupride can incorporate as much as~30 mol % of a "PtCu" component, apparently without relevant modification of the unit cell.…”

Unnamed Pt(Cu0.67Sn0.33) from the Bolshoy Khailyk River, Western Sayans, Russia, and a Review of Related Compounds and Solid Solutions

“…19)Σ0.98S1.02, a bornite-like phase, (Cu4.06Fe1.47)Σ5.53S4.5, and a godlevskite-like phase, Ni9.5S7.5. Less common and rare minerals include sperrylite, a zoned oxide Ru6Fe 3+ 2O15, and an uncommon variety of seleniferous and rhodiferous sperrylite (Pt,Rh)(As,Se,S)2 [1,10].…”

“…The density could not be measured owing to the small The sulfide species observed in the placer are members of the laurite-erlichmanite series, cooperite, bowieite (Cu-rich), a monosulfide-type phase, (Fe 0.40 Ni 0.39 Cu 0.19 ) Σ0.98 S 1.02 , a bornite-like phase, (Cu 4.06 Fe 1.47 ) Σ5.53 S 4.5 , and a godlevskite-like phase, Ni 9.5 S 7.5 . Less common and rare minerals include sperrylite, a zoned oxide Ru 6 Fe 3+ 2 O 15 , and an uncommon variety of seleniferous and rhodiferous sperrylite (Pt,Rh)(As,Se,S) 2 [1,10].…”

“…They include (1) natural solid-solutions pertaining to the system PtNi-PtFe-PtCu and the synthetic analogues of PtFe and PtNi (e.g., [4,5,[16][17][18]; (2) potarite, PdHg, and its synthetic equivalent [19][20][21][22], as well as an auriferous variety of potarite, Pd(Hg,Au) [23]; and (3) tetra-auricupride, AuCu ( [24], cf. [18]) and its variants having platiniferous compositions: (Au,Pt)Cu, e.g., [10].…”

Gold in Irish Coal: Palaeo-Concentration from Metalliferous Groundwaters

“…Gold enriched with platinum has also been identified in drainage and overburden derived samples from Lower Devonian sediments and in minor volcanic rocks of Devon, SW England, considered to have grown from oxidising saline fluids at approximately 100 • C [64]. Gold-platinum-copper alloys have also been described in Russia [65,66] in the placer of the Konder alkaline-ultrabasic massif [65] and in the alluvium along the River Bolshoy Khailyk, western Sayans [66]. Although rare, platinum enrichments are recorded in coal where a source is available [9].…”