How is it possible for percolating groundwater to remove mineral material as well as deposit it?

Percolating water can both remove mineral materials as well deposit it. Percolating water removes the undesirable materials from the rocks that come in its contact. In this way it erodes the surface of the rock and deposits it on the upper layer of the soil, thus enriching the soil.
Similarly the desirable materials are removed from the surface and deposited and concentrated. These processes are referred as secondary enrichment.