Another type of hydrothermal deposit is associated with divergent plate boundaries where active volcanism occurs along mid-oceanic ridges. Recall from Chapter 4 that in areas of active seafloor spreading how basaltic magmas create new oceanic crust along extensive ridge systems on the ocean floor. As illustrated in Figure 12.8, heat from shallow magma bodies causes hydrothermal fluids to flow upward through fractured rocks within the ridge; the fluids are replaced by cold seawater flowing downward along the flanks of the ridge. This convective motion is believed to cause strong chemical reactions between seawater and the basaltic rocks, generating hydrothermal fluids rich in copper, lead, and zinc. As the hot fluids discharge along the crest of the ridge, the dissolved metals react with cold ocean water to form sulfide minerals, producing a thick mineral deposit called a massive sulfide deposit. Notice