Variscan cycling of gold into a global coal reservoir

The potential of coal and coal ash as a source of strategically and/or commercially valuable trace elements, including gold, is reflected in numerous analytical studies, reports to government, patents for new technology and the first commercial extraction facilities. It is shown here that there was a particular predisposition to the concentration of gold in the Upper Carboniferous (313-304 Ma) Carboniferous coals that dominate coal supplies in the northern hemisphere. Coal was deposited in foreland and other basins adjacent to the actively colliding Variscan-Alleghanian Orogen, while the orogenic belt was mineralized by gold ore from 410 to 310 Ma over 10,000 km from the Appalachians to China. High gold fertility in the orogenic belt, the additional concentration of gold along shear zones during transpression, and either rapid erosion ( > 1 km/Myr) of the orogenic belt into adjacent basins or hydrothermal mineralization of the basins, made the coals a trap for the consequent flux of gold. This cycling of gold is evidenced by enriched coal and gold palaeoplacers in coal-bearing sequences in numerous basins along the orogen. Provenance data, especially detrital zircon ages of 350-300 Ma, help to identify successions that were sourced from gold-rich terrains, and thus can focus the search for anomalously enriched coal.