Dear Bhattacharya!

This is a good question ;) In natural environments above 300°C, organic complexes are dissociated and are unlikely to be important in high-temperature ore fluids (Misra, K.C.1999. Understanding Mineral Deposits). Probably one of the most comprehensive literature in this topic is: Pittmann, E.D., et al (eds.) 1994.Organic Acids in Geological Processes.

However about experimental data, Au(CO)Cl and in concentrated H2SO4, the ions Au(CO)+ and Au(CO)2+ are stable under "normal" P-T conditions, but whether they may be exist in natural hydrothermal systems is a good question too...;)

Have a good searching!

best wishes,

Viktor

Dear Sourabh

I don’t have an answer for your question, and the scarcity of constraints on the solubility of metals in CO2 is a fact. However, my comment is about the possible role of CO2 in ore formation. CO2 is a very common gas in hydrothermal fluids, but the chemical bonding between gold and CO2 species is weak. The presence of CO2 in solution affects (1) the liquid-vapor relationships, enhancing the immiscibility field of the fluid system (facilitates unmixing and creates a separate vapor phase, which, in turn, might move sulfur and chlorine species to the vapor, which will then act as ligands for metals), and (2) pH solution and gold solubility.

Maybe you can find some answer in the references below

Higgins, N.C., 1980. Fluid inclusion evidence for the transport of carbonate complexes in hydrothermal solutions. Canadian Journal of Earth Sciences 17, 823–830.

Keppler, H., Wyllie, P.J., 1990. Role of fluids in transport and fractionation of uranium and thorium in magmatic processes. Nature 348, 531–533

Lowenstern, J.B., 2001. Carbon dioxide in magmas and implications for hydrothermal systems. Mineralium Deposita 36, 490–502.

Phillips, G.N., Evans, K.A., 2004. Role of CO2 in the formation of gold deposits. Nature 429, 860–863.

Pokrovski et al. 2014 Gold speciation and transport in geological fluids: insights from experiments and physical-chemical modeling. Geol Society of London Special Pub 402

kind regards

Evandro