Modelling Mesoarchaean climate: Economic implications

The Witwatersrand Basin on the Kaapvaal Craton hosts the world’s largest gold province, with the vast majority of gold concentrated in the 2.90–2.79 Ga Central Rand Group, whereas the slightly older 2.95–2.91 Ga West Rand Group is largely barren despite comparable sedimentary characteristics. This contrast has been attributed to intensified chemical weathering during Central Rand Group times, which promoted enhanced gold mobilisation from the Archaean hinterland. However, the climatic and environmental drivers of this weathering intensification remain poorly constrained. To address this, we investigated Mesoarchaean climate controls using the Planet Simulator (PlaSim), an Earth system model of intermediate complexity. We conducted 140 PlaSim simulations to quantify the climatic sensitivity to atmospheric greenhouse gas concentrations, continental surface area, surface albedo, and land configuration. CO₂-equivalent concentrations (3–30 %), land coverage (8–28 %), and albedo (0.15–0.30) were systematically varied across different land distributions (equatorial, polar and spread over different latitudes).

Next to the well-known effect of global warming under increased greenhouse gas concentrations, our results show that increasing continental area generally results in global cooling due to the higher albedo of land surfaces relative to oceans, particularly when land was concentrated at low latitudes. This cooling effect becomes pronounced once land exceeds approximately 13 % of Earth’s surface. At high latitudes, land has minimal climatic impact because of the low incoming radiation angle that leads to less absorption. Exceptions are noted under conditions of low greenhouse gas concentrations and low surface albedo, at which limited land growth could slightly enhance warming. Among the tested land positions, the scenario with land spread over different latitudes resulted in the highest climate sensitivity.

Overall, our results indicate that land distribution alone was unlikely to have caused global warming during the Mesoarchaean, and this climatic influence was probably dampened by a more rapid carbon cycle at that time. Instead, elevated atmospheric greenhouse gas levels emerge as the dominant driver of warming and enhanced chemical weathering. The climatic transition around ~2.9 Ga may further reflect the emergence of extensive low-albedo mafic or ultramafic surfaces and/or the latitudinal migration of the Kaapvaal Craton into a more radiatively sensitive, low-latitude zone. These combined factors likely contributed to intensified weathering, increased gold leaching, and the gold megaevent responsible for the formation of the Witwatersrand ores.