in Figure 12.8 that sulfide deposits called black smokers or chimneys form where the hydrothermal fluids discharge from the seafloor.
Massive sulfide deposits have long been important sources of copper, lead, and zinc. These deposits are quite ancient and there is much geologic evidence to suggest that some found on land today have originated along oceanic spreading centers. It is believed that some sulfide deposits are now exposed on land because of simple tectonic uplift, whereas others may have been welded onto an existing landmass when an oceanic plate descended into a subduction zone. A good example is the island of Cyprus in the Mediterranean, where a massive sulfide deposit has been an important source of copper for nearly 4,000 years. In fact, the word copper itself is derived from the island’s original Greek name of Kupros. Cyprus was one of the ancient sites where people made copper implements from pure copper metal found at the surface. After exhausting the supply of pure metal, people continued to obtain copper by placing copper-sulfide minerals into a large fire. The intense heat would cause the chemical bonds within the minerals to break, resulting in molten copper draining into a pit at the base of the fire.
FIGURE 12.5 Dense minerals that are the first to crystallize can settle to the bottom of a magma chamber and form a layered ore deposit (A). The photo (B) shows layers of chromium-rich minerals that are part of a layered intrusion in Bushveld, South Africa.