The term supergene is used to describe processes and products that are the result of near-surface alteration and modification of originally deeply formed rocks. It is in the critical zone – the Earth’s contact zone where air, water, biota, organic matter, and minerals interact – where combinations of geological, chemical, physical, and biological processes operate together on preexisting minerals so as to adjust to the new environmental conditions (average T_atm ~15 °C, P_atm ~1 bar, and pO₂ ~ 0.2 bar) (Reich and Vasconcelos, 2015).

Supergene processes are controlled by three basic factors. The first and most important factor is the parent rock (e.g., limestone vs. andesite) and its mineral constituents (e.g., silicates vs. sulfides). The second factor is landscape , which is shaped by hydrological and pedological processes coupled with the geodynamic evolution of the crustal section under consideration. The third factor is climate ,...