40Ar/39Ar dating of exceptional concentration of metals by weathering of Precambrian rocks at the Precambrian-Cambrian boundary

The sub-Cambrian surface, including diverse metalliferous deposits, shows evidence of intense weathering of Precambrian rocks to form supergene-enriched ores and metalliferous placers, followed by widespread peneplanation. Much of the metal would have been flushed to the Cambrian ocean during peneplanation. An 40Ar/39Ar age of 542.62 ± 0.38 Ma (1 sigma, full external precision, Renne et al., 2011) for metalliferous alteration clays in Scotland shows that this event occurred immediately prior to the Precambrian-Cambrian boundary. A negative δ53Cr isotopic signature for the clay is consistent with mobilization on land of redox sensitive metals by oxidative terrestrial weathering. This unprecedented flushing of metals from the weathered Precambrian surface would have contributed to the chemistry of the earliest Cambrian ocean at a time of marked faunal evolution.