"Manganese nodules occur in all the oceans. Their accretion rate is very slow, only a few mm in 1 million years. The average nodule has 24% manganese, compared to 35 to 55% manganese in land ore bodies, so they do not offer solid economics as a manganese source, but they also contain iron (14%), copper (1%), nickel (1%), and cobalt (0.25%).

Polymetallic Sulfide Deposits
Polymetallic sulfide deposits are products of the circulation of seawater through the hot volcanic rocks which well up along spreading ridges of the oceans and back-arc basins. Upon coming in contact with cooler water, the minerals precipitate producing mineral deposits of zinc, copper, lead, barium, silver, and gold in widely varying proportions in sulfides and oxides. Some deposits in heavily sedimented environments appear to contain several millions of tons of ore and compare with some of the largest massive sulfide deposits that are being mined on land. Except for the Atlantis II Deep in the Red Sea, none of the deposits have been surveyed and sampled sufficiently to determine their grade and tonnage. "
http://geology.uprm.edu/Morelock/resdeep.htm

On earth land surface, primate people of found gold and there was what is called native copper [copper as metal not ore]. Not sure how long native copper would last in salt water, but I see no reason why gold nuggets couldn't be found in oceans