Mobility of Dissolved Palladium and Platinum Species during the Water–Rock Interaction in a Chloride Environment: Modeling of PGE Behavior during Interaction between Oceanic Serpentinites and Seawater Derivatives

—The palladium and platinum behavior was simulated under conditions of low-temperature hydrothermal alteration of oceanic crust serpentinites in order to reveal the possibility of PGE transfer by highly saline chloride solutions. Flow-through water–rock experiments performed using columns filled with crushed ultrabasic rocks of ocean floor (variably carbonated harzburgitic serpentinites of MOR) showed that the efficiency of the palladium transfer depends of the degree of alteration (carbonation) of peridotites and is 80–100% under experimental conditions. It is suggested that palladium is transferred as a strong complex compound with thiosulfate ion, which represents the intermediate oxidation product in the “sulfide–sulfate” system. Platinum hydrolyzing under near-neutral pH conditions and forming no compounds with thiosulfate-ion is completely retained by serpentinites likely owing to the sorption interaction with silicates. Thus, it was confirmed that palladium is highly mobile during the low-temperature alteration of abyssal peridotites, and its distribution in the studied rocks depends on the serpentinization and carbonation.