The worldwide occurrence of Au ores associated with Phanerozoic strata reveals a bimodal temporal association with either older Paleozoic or younger Mesozoic successions. These strata were deposited mostly in passive-margin environments synchronously with formation of volcanogenic massive-sulfide ores on active margins, during times of high sea level, widespread submarine oceanic volcanism, reduced and, at least locally, sulfidic oceans, and episodes of ocean anoxia. This correspondence of ocean properties and ages of strata that host Au seems beyond coincidence. Cause and effect cannot yet be described with confidence, but beyond the evolution of chemically reduced strata, the reduced oceans may also have been favorable to the enhancement of Au in certain strata that may constitute metallotects of Au.

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