Experimental Study of Pt Solubility in the CO-CO2 Fluid at Low fO2 and Subsolidus Conditions of the Ultramafic-Mafic Intrusions

Abstract

The solubility of Pt in CO-CO2 fluid was studied experimentally at P = 50–200 MPa and T = 950 °C. A mixture of MgC2O4 and MgCO3 was used as a source of the fluid. Upon the reaction of the Pt capsule walls and the fluid, a carbonyl of platinum is formed. The use of the high-temperature quartz ceramics as a fluid trap avoids the effect of mechanical contamination with Pt from the eroded capsule walls. The total content of platinum in the porous fluid traps was measured by the Electrothermal Atomic Absorption (ET-AAS) method. In some experiments, the local analysis of traps was carried out by the Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) method. The composition of fluid in bubbles captured in an albite glass trap was studied by micro-Raman spectroscopy. On the capsule walls and MgO, Pt “whiskers” of submicron diameter were observed, which were formed as a product of carbonyl decomposition during quenching. About 5–15% of carbonyl withstands quenching resulting in 1.5 to 2 ppm Pt soluble in acetone (runs at P = 200 MPa) in a quartz glass trap. The amount of Pt soluble in acetone from the capsule walls corresponds to a concentration of up to 8 ppm in the fluid. A high content of soluble Pt of 2000–3000 ppm was determined in a carbon coated MgO matrix. Our study demonstrated that the solubility of Pt in the CO-CO2 fluid is 15–150 ppm, presumably in the form of Pt3(CO)62− under conditions corresponding to the conditions of the subsolidus stage of layered ultramafic-mafic and ultramafic-alkaline intrusions formation. Our preliminary data showed that this solubility will increase with the addition of water at low fO2.

Editorial for Special Issue “Mineralogy of Noble Metals and ‘Invisible’ Speciations of These Elements in Natural Systems, Volume II”

“…Simakin et al [14] performed an experimental study of Pt solubility in a CO-CO2 rich fluid at PT conditions close to the subsolidus conditions of upper crust ultramafic-mafic intrusions. They demonstrated that the solubility of Pt in a CO-CO2 fluid at 50-200 MPa and 950 • C is 15-150 ppm, presumably in the form of Pt3(CO)62−.…”

The petrology of the J-M Reef Pd-Pt deposit and the Lower Banded series of the Stillwater Complex, Montana, USA

“…Braun et al (1994) concluded that this meant that the comparison of whole-rock compositional data for pegmatoidal rocks and their The pegmatoidal textures of both the Merensky Reef and J-M Reef have been pointed to as evidence of the generation of high-grade reef-type mineralization by upward-migrating volatile-rich fluids that scavenged metals and PGE from underlying mush and deposited them at the level of the reef (Boudreau, 2020 and references therein). Experimental work has shown that PGE are soluble in volatile-rich fluids under certain conditions and could play some role in redistributing PGE in mafic intrusions (Wood, 1987;Simakin et al, 2021;Sullivan et al, 2021aSullivan et al, , 2021b. However, thermodynamic calculations of the solubility of PGE as chloride complexes in a vapor phase indicate that Ni, Cu, and Fe are several orders of magnitude more volatile than the PGE and thus enrichment of PGE enrichment over Ni and Fe is not accounted for by vapor transport models (Wood, 1987).…”