Applied mineral exploration methods, hydrothermal fluids, baro-acoustic decrepitation, CO2 rich fluids
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Thermodynamic studies show that Au is NOT transported in pure CO2 fluids

Kingsley Burlinson:  November 2016

Since 1997 assertions have been made that gold might be transported in and deposited from pure CO2 (non-aqueous) fluids. These assertions have been based on incorrect interpretation of CO2 only fluid inclusions within quartz, supposedly lacking contemporaneous H2O fluid inclusions.

Recently (2015)  Liu et. al. have undertaken thermodynamic studies, including gold solubility experiments, to measure the solubility of gold in pure CO2 fluids. They presented a paper at the Goldschmidt conference in 2015 and their data indicates that gold does NOT dissolve in pure CO2 fluids and that hydrated chloride species transport the gold.

In 1997 Schmidt-Mumm et. al. published a paper on a fluid inclusion study at the Ashanti gold mine, Ghana. They recognised pure CO2 fluid inclusions and did not identify any associated aqueous inclusions. They cursorily dismissed the possibility of trapping from a  heterogeneous fluid (a physical mixture of liquid water and CO2 gas bubbles) and asserted that gold could perhaps be transported in super-critical anhydrous CO2 fluids. I have discussed this erroneous research in 4 other sections on this website and shown conclusively that their own photographs of their fluid inclusion samples prove that heterogeneous fluids containing water and CO2 gas bubbles were present and that the assertion of gold transport in anhydrous CO2 fluids was unsubstantiated.

  1. Fluid inclusions in quartz cannot prove that non-aqueous fluids CO2 formed the ore

    A discussion of the critical necessity to explain the transport of quartz, which was ignored in that research.
  2. Gas dominated inclusion assemblages may be trapped from aqueous dominant heterogeneous fluids by disproportional trapping

    A explanation why heterogeneous fluids do not trap inclusions from all phases or in proportion to their phase abundance.
  3. Spherical or well rounded gas-filled fluid inclusions prove that heterogeneous trapping occurred from a dominantly liquid phase fluid.

    A proof that pure gas fluid inclusions were actually trapped from heterogeneous water-CO2 fluids and NOT from homogeneous anhydrous CO2 fluids.
  4. Contrasting types of heterogeneous fluids. Boiling versus gas-rich aqueous immiscibility systems.

    A discussion of heterogeneous fluid systems and the often-overlooked additional complexity due to immiscible phases such as CO2.

Following after that 1997 publication, pure CO2 fluid inclusions were found in other gold deposits, most notably Campbell-Red Lake in Canada, and these were also mis-interpreted to indicate gold transport in anhydrous CO2 fluids. The lack of critical analysis of the conclusions in these studies led to the funding and conduct of research into the thermodynamic behaviour of gold in super-critical CO2 fluids at CSIRO in Canberra, Australia.

This research work by Liu is summarised in the abstract of the paper presented by them at the Goldschmidt conference in 2015.
The authors conducted autoclave experiments and determined that gold solubility decreased as the CO2 mole-fraction of the fluids increased. They also carried out Molecular Dynamics simulations and concluded that "H2O as a polarized molecule plays a more active role than the un-polarized CO2 molecule in the fluids, and hydrated chloride species are the main form for transporting gold in the CO2-H2O-HCl system."


The thermodynamic and experimental study of super-critical CO2 fluids indicates that gold is not transported in these fluids. This confirms the prior rebuttal of such gold transport in the discussions listed above on this website. The interpretation of anhydrous CO2 fluid inclusions has been confused by the serious failure to understand heterogeneous fluid systems in which there is an immiscible fluid component (CO2). Such fluid systems behave quite differently to the single component boiling water heterogeneous fluid systems which are the basis for almost all of the literature discussions of heterogeneous fluids. The discussions on this website, listed above, have long since pointed out this error and are confirmed by this recent thermodynamic study.