Transport Of Platinum-group Elements Research Articles

Hydrothermal transport of PGEs in porphyry systems – a fluid history of the Skouries Cu–Au (PGE) porphyry deposit

Porphyry deposits are a potential alternative resource for platinum group elements (PGEs), as well as critical metals such as Te, Se and Bi. The Skouries deposit is a PGE-enriched Au–Cu porphyry sy...

Vertical Alignment of Educational Opportunities for STEM Learners: Evaluating the Effects of Road Dust on Biological Systems

In efforts to develop a unique pedagogy for underrepresented high school and undergraduate students, we developed a pilot study to determine the effectiveness of vertically integrating STEM research education from high school students through Ph.D. candidates. The interdisciplinary research project's overarching goal is to assess the impact of environmental pollutants (specifically, platinum group elements found in road dust) on eukaryotic and prokaryotic cells and develop computational models to predict the outcomes of exposure. Ultimately, the project involves elements of fate and transport of platinum group elements in soil, water, and air and their impacts on environmental microbiology, eukaryotic cell signaling, and environmental computational modeling. Our vertically integrated and aligned mentorship model paired high school students with undergraduates, M.S. students, and Ph.D. students in various laboratories. To complement their laboratory research exposure, students also attended professional development seminars on résumé preparation, literature mining/searching, preparation of manuscripts, presentation of data, and critical reading of peer-reviewed articles. Our pilot study was very successful in exposing future STEM workers (high school students and college undergraduates) to meaningful research experiences that they translated into seven poster and oral presentations, three review articles (in preparation), three journal articles, and improved attitudes toward STEM careers.

Experimental observations on noble metal nanonuggets and Fe-Ti oxides, and the transport of platinum group elements in silicate melts

Platinum group element (PGE) nanonuggets are a nuisance in experimental studies designed to measure solubility or partitioning of noble metals in silicate melts. Instead of treating nanonuggets as experimental artifacts, we studied their behaviour motivated by recent discoveries of PGE nanonuggets in a variety of natural settings. We used an experimental setup consisting of AgPd, Pt or AuPd capsules and Fe(-Ti) oxide-saturated hydrous peralkaline silicate melts to maximise nanonugget production. TABS (Te, As, Bi, Sb, Sn) commonly occur in PGM (platinum group minerals), prompting addition of Bi to our experiments to investigate its properties as well. Three-dimensional optical examination by 100× objective and immersion oil reveals variable colour which correlates with nanonugget size and shape due to plasmon resonance effects. We observe two textural types: (1) intermediate-sized nanonuggets dispersed in the glass and adhering to oxides, and (2) abundant fine nanonuggets dispersed in the glass with coarse euhedral crystals in contact with oxides. Slow cooling removes dispersed nanonuggets and greatly coarsens existing oxide-associated metal crystals. Nanonugget-free halos are commonly observed around oxide grains. All metal phases are composed of major (Ag, Pd) and trace (Pt, Ir, Au) capsule material.Our results show reduction processes, imposed by growing oxides, causing local metal saturation in the oxide rich zones with preferential nucleation on smaller oxide grains. The redox gradient then blocks additional metals from diffusing into oxide rich zones, forming halos. As the entire experimental charge is reduced throughout the run, nanonuggets form in the distal glass. Bismuth contents of metal phases do not depend on Bi2O3 amounts dissolved in the melt. Further PGM crystallisation consumes nanonuggets as feedstock. We conclude that the appearance of metallic PGE phases happens in two stages: first as nanonuggets and then as larger PGM. Once formed, nanonuggets cannot be removed by oxidation or dissolution, but only by PGM coarsening.Sulfur-poor PGE ore deposits commonly contain more PGE than permitted by existing estimates of equilibrium solubility in silicate melts. This is commonly explained by initial scavenging of PGE by sulfide liquids followed by S-loss, but evidence for S-loss is not conclusive. We suggest that nanonuggets may be a means to transport PGE from source regions to form ore deposits, followed by direct PGM crystallisation from silicate melt without intermediate concentration by sulfide liquids.

Environmental Relevance of the Platinum-Group Elements

Platinum-group elements (PGE) are used in an increasing number of applications, and emissions are resulting in elevated environmental concentrations of these normally rare metals. Automobile exhaust catalysts, which use Pd, Pt, and Rh as active components, are the main source of PGE emitted into urban and roadside environments, and they contribute to a global increase in PGE concentrations. Emitted PGE are found in urban air and accumulate on the road surface and in roadside soil. Transport of PGE via stormwater is resulting in contamination of aquatic environments. There is now mounting evidence that a fraction of PGE in the environment is bioavailable, and potential uptake into the biosphere is raising concern over potential risks for humans and the environment.

NEW DATA ON "BONANZA"-TYPE PGE MINERALIZATION IN THE KIRAKKAJUPPURA PGE DEPOSIT, PENIKAT LAYERED COMPLEX, FINLAND

Various platinum-group minerals (PGM), phases rich in the platinum-group elements (PGE), and unusual species occur in the Kirakkajuppura area, Penikat layered complex, Finland. The PGM are intimately associated with actinolite and clinochlore. The base-metal sulfides [chalcopyrite, millerite, bornite, chalcocite, ferroan chalcocite(?), digenite or roxbyite: Cu9S5] are in minor or trace amounts. The observed PGM and rare species are: vysotskite–braggite series [PdS–(Pt,Pd)S], zvyagintsevite [Pd3Pb], a zvyagintsevite-like phase [(Pd,Pt)3(Pb,Cu)], unnamed Pd–Pb oxide [Pd7PbO8 or Pd3.5Pb0.5O4], various Cu–Fe–PGE thiospinels (large grains and unusual micro-aggregates), laflammeite [Pd3Pb2S2], laurite–erlichmanite series [(Ru,Os,Ir)(S,As)2 –(Os,Ru,Ir)(S,As)2], irarsite–hollingworthite series [(Ir,Rh,Ru)As1− x S1+ x – (Rh,Ir,Ru)As1− x S1+ x ; x ≤ 0.2], konderite-like Pb–(Pd)-rich sulfides and a Fe-dominant analogue of konderite [(Cu,Ni,Fe)3+ x (Fe,Pb)(Rh,Ir,Pd)8− x S16; x < 0.5], unnamed Rh1− x (Ni,Fe,Cu)2+ x S3 (0 ≤ x ≤ 0.1), a Pd–Pt–Cu alloy [Pt-rich, Cu-rich palladium: Pd89.42–91.22Pt5.94–6.16Cu2.62–4.64], skaergaardite–hongshiite [(Pd0.92 Pt0.10)∑ 1.02Cu0.98], keithconnite [Pd20(Te,Bi)7], plumbian keithconnite [Pd20(Te6Pb)], unnamed Pd5(As,Te,Sn,Pb)2, Pd-rich, Cu-rich gold [Au76.1–81.1Pd13.7–16.0Cu6.1–6.3Ag1.2–3.4], Zn-rich copper (natural?), unnamed Pb4O(VO4)2, and an undefined Pb-rich iron silicate (hydrous?). In addition, unnamed (Th,Ca)(V5+,Si,P)O4 and associated baddeleyite, barite, and a phosphatian huttonite or thorite occur in a pegmatitic gabbro from Kirakkajuppura. The Kirakkajuppura PGE mineralization probably formed by efficient hydrothermal remobilization and transport of PGE from their “primary” zones [Pd–Pt zones associated with the low-sulfide SJ reef and Ru–Os-mineralized chromitite zones], resulting in the local deposition of the extremely S-poor, PGE-rich assemblage, which is intimately associated with hydrous silicates and is located near the northern end of the Penikat complex.

Solubility and transport of platinum-group elements in supercritical fluids: summary and estimates of thermodynamic properties for ruthenium, rhodium, palladium, and platinum solids, aqueous ions, and complexes to 1000°C and 5 kbar

Several correlation methods are used to estimate data and equation-of-state parameters that permit calculation of standard state thermodynamic properties at high pressures and temperatures for metals, oxides, and sulfides, as well as ions, and aqueous chloride, hydroxide, and sulfate complexes of Ru +2, Ru +3, Rh +2, Rh +3, Pd +2, and Pt +2. Estimates are based on a critical review of data from the literature at 25°C and 1 bar. The combined data for 14 minerals, 6 cations, and 56 aqueous complexes provide a foundation for quantitative predictions of aqueous speciation of these platinum group elements (PGE), as well as platinum group mineral (PGM) solubilities as functions of pH, oxidation state, and chloride and sulfate content of geologic fluids at temperatures to 1000°C and pressures to 5 kbar. Therefore, these estimates are the first to address PGE speciation at the pressure and temperatures of most PGM deposits. Comparisons are made to other theoretical predictions of platinum-group element (PGE) complex formation in aqueous solutions and to pertinent experimental data. We conclude that Pd-chloride complexes may be less stable at lower temperatures than previously predicted by other investigators, but that Pt-chloride complexes may be considerably more stable.

Platinum genesis; new mineralogical evidence

The two distinct types of platinum deposits in the Bushveld Complex (reefs and pipes) differ in relative age, geological position, and mineralogy. Reefs are characterized by the association of braggite, cooperite, laurite, and sperrylite with platinum-iron alloy and minor Pt-Pd bismuthotellurides and pipes by platinum-iron alloy, sperrylite, geversite, and Rh-Ir sulfarsenides. There are distinct regional variations in platinum mineralogy within the Merensky Reef; these are, however, largely confined to the relative proportions of the constituents. The pipes differ in the actual minerals present.The Sudbury and Stillwater deposits show a prevailingly higher content in compounds of Pd, Pt, Bi, Te, and S. This can be explained by the general tendency of Pd to associate preferentially with sulfides in the earlier stages and to form independent platinum-group minerals in the later stages of the magmatic cycle. Serpentinization plays an active role not only in the conversion of silicate nickel into sulfide nickel, but also in the extraction of platinum-group elements from silicates, oxides, and sulfides, and in their localization as independent and economically significant platinum-group minerals. Hydrothermal copper-platinum ores not spatially related to basic igneous rocks emerge as a separate genetic type.Investigation of placer deposits from worldwide localities shows that (1) placers linked to alpine-type ultrabasic massifs carry significant amounts of Pt as well as iridosmine and osmiridium; (2) inclusions in native alloys and sperrylite may provide information on the mineralogy of primary deposits--michenerite and hollingworthite in Urals placers are a case in point; and (3) alteration of platinum-group element alloys in placers is a widespread process which takes place at surface temperatures. Placers derived from Neogene ultrabasics in Japan carry textural types similar to those found in Precambrian Witwatersrand platinum-group mineral concentrates.The formation of platinum deposits is dominated by polyphase processes which also include transport of platinum-group elements in aqueous solutions.