How do dissolved minerals that form chemical rocks enter the ocean?

Rivers bring the dissolved minerals to the ocean. Over the course of their flow (over land), river water dissolves the minerals from the strata of the channel. Rivers also receive the water from a number of smaller streams, which may similarly contain the dissolved minerals and hence contribute to the mineral content of the river itself. Finally, the surface runoff (water flowing over the land surface) in the river basin also contributes water (and hence minerals) to the river.
Some of these minerals may be deposited by the river when the river's velocity decreases as it is about to enter an ocean. The remaining minerals are then added to the ocean. 
These dissolved minerals may precipitate out of the water and form chemical rocks. Thus, it is the rivers that carry the dissolved minerals all the way to the ocean.
Hope this helps.