S.I. TURCHENKO (IPGG RAS)

Gold in the seawater of Precambrian oceans: application to Au deposits formation

Oceanic carbonaceous deposits adsorb gold from seawater during sedimentation and diagenesis, and Au has formed part of sedimentary pyrite starting from 3.5 Ga. Water of the Meso- and Neoarchean oceans contained several times more Au than modern oceans. Au grade in the water of the oceans decreased, particularly after a global oxidative event in the Paleoproterozoic, and then slowly increased again in the Neoproterozoic (from 800 to 520 Ma). In the Archean and Proterozoic, the Au grade in the seawater is correlated with the time of the distribution of high-Mg basalts, komatiites and black shales in greenstone belts. Oxygen increase in the Earth’s atmosphere is combined with a low Au background in komatiites and Mg basalts, which previously enriched the seawater with gold. This is also indicated by the absence or insignificant amount of gold deposits in the period of 1600–800 Ma, which can be explained by low Au grade in the water of the oceans during this age period.
Keywords: Au in Precambrian seawater, Proterozoic distribution of Au deposits, basalt, komatiite.