Hydrothermal fluids will normally deposit minerals in concentrated masses or in a dispersed manner throughout a rock body as shown in Figure 12.7. For example, vein deposits occur when ore minerals crystallize from the hot fluids and fill fractures and small fissures within rocks. Vein deposits are commonly considered to be high-grade deposits because the ore minerals are highly concentrated. In addition to filling fractures, hydrothermal fluids will also move through the country rocks in a diffuse manner, resulting in low-grade deposits where the ore minerals are widely dispersed in what are known as disseminated deposits. Note in Figure 12.7 that disseminated ores can be found in both the intrusion and the surrounding country rocks. Some of the world’s largest surface mines involve removing massive bodies of rock where the disseminated copper minerals are so small that they cannot be seen with the naked eye.