Some gold ores are associated the Phanerozoic ocean strata. These strata are believed to have been laid down on the ocean floors during periods of deep sea anoxia (Keith 1982, Spencer 1991). Most of these deposits are associated with the passive-margin environments of the lower Paleozoic and the upper Mesozoic eras. Since these strata and anoxia events are also associated with periods of high ocean levels, it is believed that oxygen the minimum zone, currently between at 500 to 1000 meters in depth, extended to the deep seafloors. It is believed that the increase in global temperatures and sea levels at these times interrupted the deep currents that carry the cold oxygen rich currents from the polar regions down to circulate around the ocean basins. The lack of oxygen in the deep ocean caused an enrichment of the sulfide elements and minerals associated with ocean volcanic activity (Spencer 1991).