Hydrocarbons as ore fluids

Abstract

Conventional wisdom holds that aqueous solutions are the only non-magmatic fluids capable of concentrating metals in the Earth's crust. The role of hydrocarbons in metal concentration is relegated to providing geochemical barriers at which the metals are reduced and immobilised. Liquid hydrocarbons, however, are also known to be able to carry appreciable concentrations of metals, and travel considerable distances. Here we report the results of an experimental determination of bulk solubilities of Au, Zn, and U in a variety of crude oils at temperatures up to 300 °C and of the benchtop-scale transport experiments that simulate hydrocarbon-mediated re-deposition of Zn at 25-200 °C. It has been demonstrated that the metal concentrations obtained in solubility experiments are within the range of concentrations that are typically considered sufficient for aqueous fluids to form ore bodies. It has also been shown that Zn can be efficiently transported and re-deposited by hydrocarbons. These results provide direct evidence of the ability of natural crude oils to mobilise metals available in hydrocarbon-associated host rocks, and transport them in concentrations sufficient to contribute to ore-forming processes.