Properties of Reduced Carbon Dioxide Fluid: Evidence from Experimental and Thermodynamic Modeling

Abstract

It is shown experimentally that fluid mostly consisting of CO₂ and CO is a good solvent for many petrogenic and ore components under high P–T parameters. Siderite decomposed to oxides and a mixture of CO₂ and CO was the source of the fluid in the experiment. It is demonstrated that an ultrapotassic alkaline melt was formed on the oxide matrix as a result of fluid transport of the components of the basaltic melt at 2–5 kbar and 900–1000°C. This melt is characterized by high concentrations of Rb, LREE, Sr, and Ba. The mechanism of solubility of metals in the carbon dioxide–reduced fluid includes the formation of volatile carbonyls. As is evident from thermodynamic modeling, the stability of Ni(CO)4 at high pressure reaches magmatic temperatures. The finding of native nickel in aerosols during eruption of the Tolbachik Volcano in 2012–2013 is explained by decomposition of carbonyl from fluid of a deep origin during magma ascent.