Got this from the net.....
Most of the ocean's salts were derived from gradual processes such
the breaking up of the cooled igneous rocks of the Earth's crust by
weathering and erosion, the wearing down of mountains, and the
dissolving action of rains and streams which transported their
mineral washings to the sea. Some of the ocean's salts have been
dissolved from rocks and sediments below its floor. Other sources
of salts include the solid and gaseous materials that escaped from
the Earth's crust through volcanic vents or that originated in the
atmosphere.
