With What Are Ore Deposits Associated?

Geological Association

• Mineral deposits are associated with geological action. Volcanic action forms mineral deposits. In the igneous process, heavy ores crystallize in magma and settle to the bottom of magma chambers. When magma explodes upward from these pipes, ore is pushed to the surface. Plate tectonic action melts and churns rock, leaving deposits of minerals in rift, convergent plate margins, basin and dome areas. Hydrothermal deposits are formed when magma heats groundwater flowing through it and dissolves metals which are deposited in veins. Sedimentary settling of minerals in water also leaves deposits of minerals behind in the sediments, which become ore bearing rock. These actions often leave signs of ore deposits in the texture of the surface rocks.

Surface Texture Association

• Ore deposits are often recognizable from their texture. Different textures arise from different geological processes. Minerals may crustify, forming coatings or layers of minerals on other minerals or rocks. Sometimes minerals fill spaces, crevices and fractures in rocks and other minerals. Some minerals form from colloidal solutions and form banding, as may be seen in some iron ore deposits. Minerals may even replace other minerals, as happens when one or more elements in a mineral become richer over time, or one mineral overgrows another one. Becoming familiar with the textures associated with minerals helps prospectors increase their chances of finding valuable ores.

Mineral Association

• Because the formation of mineral ore is a chemical process, some minerals are likely to be found associated with other minerals. Gold is a mineral with a large number of associations. It is found with pyrite, silver, quartz, chrysocolla (a copper ore) and even with black shale. Platinum ore occurs both with gold and in chromite deposits. Sometimes spotting associated minerals is much easier than finding the mineral ores themselves. For instance, the green of malachite and blue of azurite are quickly recognizable and often accompany copper deposits. Learning which minerals occur together greatly increases your chances of finding deposits of mineral ore in the field.

Searching For Ore

• Searching for ore is a layered process. There is never a guarantee that a geological area that can be associated with an ore will actually contain that ore. Gold is associated with volcanic activity, but not all volcanoes produce gold. Once you have found an appropriate geological area you can find minerals associated with an ore but no ore itself. For instance, not all quartz is gold bearing, and neither is all black shale. The more familiar you become with associated processes, textures and minerals, the more likely you will eventually find the ore you seek.