World-class Archean orogenic gold mineralisation is often associated with hydrothermal fluids rich in CO2 and CH4. This association has been demonstrated from fluid inclusions studies in quartz associated to gold in veins (Chi et al., 2006). The presence of carbon in ore forming hydrothermal fluids has been recognised as a potential important indicator of the source of the fluids, it has also been considered as playing a role in buffering fluid pH allowing for transport of larger quantity of dissolved gold aqueous complexes in solution (Phillips and Evans, 2004). Recent work has shown that carbon may play a more important role in the formation of high-grade orebodies. In our recently published study, we observed gold nanoparticles within an amorphous carbon phase preserved in micro-inclusions in gold from high-grade orogenic deposits (Petrella et al., 2022). Such intimate association between amorphous carbon and gold raises questions on the role of carbon in ore forming processes and on gold transport mechanism. To address these questions a better understandingof the nature of the carbon in the hydrothermal orogenic fluids is needed. Investigating the nature of the carbon in the aforementioned micro-inclusion might inform in which form it was transported in the hydrothermal system. This information could help resolve the dilemma of the potential presence of hydrocarbon in the hydrothermal system and its contribution to gold transport (Gaboury, 2021). The temperatures under which these systems are formed (350° - 400°C) might not be favourable for gold transport by hydrocarbon (Crede et al., 2019; Migdisov et al., 2017). Alternatively, results could show that such complex organic molecules where not involved in the transport and deposition of gold but that much less dense volatile compounds (Parkhomenko et al., 2012) might have played a role in metallogenic processes. Both hypotheses are novel and challenge the accepted model for gold transport in hydrothermal fluids and this study raises the novel idea of considering carbon as a potential ligand for gold in Archean orogenic systems.

Reference(s)

Chi, G., Dubé, B., Williamson, K. and Williams-Jones, A.E. (2006) Formation of the Campbell-Red Lake gold deposit by H 2 O-poor, CO 2-dominated fluids. Mineralium Deposita 40, 726. 

Crede, L.-S., Liu, W., Evans, K.A., Rempel, K.U., Testemale, D. and Brugger, J. (2019) Crude oils as ore fluids: An experimental in-situ XAS study of gold partitioning between brine and organic fluid from 25 to 250° C. Geochimica et Cosmochimica Acta 244, 352-365. 

Gaboury, D. (2021) The neglected involvement of organic matter in forming large and rich hydrothermal orogenic gold deposits. Geosciences 11, 344. 

Migdisov, A.A., Guo, X., Williams-Jones, A., Sun, C., Vasyukova, O., Sugiyama, I., Fuchs, S., Pearce, K. and Roback, R. (2017) Hydrocarbons as ore fluids. Geochemical Perspectives Letters 5, 47-52. 

Parkhomenko, R.G., Morozova, N.B., Zharkova, G.I., Shubin, Y.V., Trubin, S.V., Kriventsov, V.V., Kuchumov, B.M., Koretskaya, T.P. and Igumenov, I.K. (2012) Deposition of Au Thin Films and Nanoparticles by MOCVD. Chemical Vapor Deposition 18, 336-342. 

Petrella, L., Thébaud, N., Fougerouse, D., Tattitch, B., Martin, L., Turner, S., Suvorova, A. and Gain, S. (2022) Nanoparticle suspensions from carbon-rich fluid make high-grade gold deposits. Nature Communications 13, 3795. 

Phillips, G.N. and Evans, K.A. (2004) Role of CO 2 in the formation of gold deposits. Nature 429, 860.