Summary
Some recent investigations of black shales reveal platinum-group element (PGE) concentrations in the ppm range. The low temperature nature of these mineralized sediments and their composition stimulated this first attempt to synthesize Pt- and Pd-phases in solutions at temperatures below 100°C under reducing conditions with H2S flow through the solution. Experiments under controlled Eh-pH with montmorillonite presaturated in Pd and Pt in different chloride solutions resulted in the formation of Pt- and Pd-sulphides. PtS- and PdS-stability fields are very close to each other in Eh-pH values (∼400mV, 9). These data are in good agreement with those determined for some base metal sulphides synthesized at similar temperature by other researchers.
The results may support the role of clay minerals as possible concentrators for PGE in the sedimentary environment.
Zusammenfassung
Neuere Untersuchungen der Schwarzschiefer ergeben Konzentrationen an Platingruppenelementen (PGE) in ppm-Bereich. Niedrigtemperatur-Bedingungen und die Zusammensetzung der mineralisierten Sedimente gaben den Anlaß zur erstmaligen Synthese von Pt- und Pd-Phasen in H2S-haltigen reduzierenden Lösungen bei Temperaturen unterhalb von 100°C. Bei Experimenten, die unter kontrollierten Eh-pH-Werten in unterschiedlichen Lösungen mit an Pd und Pt vorgesättigtem Montmorillonit durch-geführt wurden, konnte die Ausfällung von Pt- und Pd-Sulfiden nachgewiesen werden. Die Stabilitätsfelder der gebildeten PtS und PdS liegen nahe beieinander, bei Eh = ∼ 400 mV und pH = 9. Diese Bedingungen sind in Übereinstimmung mit den von anderen Autoren für einige Buntmetallsulfide bestimmten Daten unter ähnlichen Temperaturen.
Die gewonnenen Ergebnisse bekräftigen die Rolle von Tonmineralen beim Absatz von PGE in sedimentärem Milieu.
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Tarkian, M., Evstigneeva, T. & Gorshkov, A. Synthesis of Pt- and Pd-sulphides in low temperature (85°C) solutions buffered by clay minerals and graphite: Preliminary results. Mineralogy and Petrology 58, 71–78 (1996). https://doi.org/10.1007/BF01165764
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DOI: https://doi.org/10.1007/BF01165764