vein

When hot, mineral-rich waters surge into the faults and cracks of a host rock, depositing crystalline and metallic minerals in relatively pure, complex sheets and ganglia-like structures, geologists refer to the threads, ropes, and tabular forms as veins. The vein pattern may incorporate, as well, large, irregular nodes of the mineral. When economically valuable deposits occur in relatively close proximity to each other, the vein is sometimes referred to as a mother lode. Quartz, a mineral of little commercial value, is the ore most commonly found between layers of rock, and it’s possible to see striking examples—ribbons of such vein quartz—gleaming in the dark, metamorphic rock of Ruby Canyon on the Colorado River west of Grand Junction in Colorado Canyons National Conservation Area. Miners, of course, are more interested in vein deposits when the ores are of higher economic value, such as native metals—silver, copper, and gold—and sulphides of zinc, mercury, and lead. Iron-rich solutions of some of these latter minerals might migrate great distances underground before streaming upward and hardening in rocks closer to the surface. Well-known and storied mineral lodes would include the Comstock silver lode in Nevada; the copper lodes of Michigan’s Keweenaw Peninsula; the Homestake gold deposits in South Dakota’s Black Hills; and silver, lead, zinc, and nickel deposits around Coeur d’Alene, Idaho. Related terms include ore shoot, a ribbonlike column of ore within the ore-bearing rock; ore body, the well-defined mass of a mineral deposit; and bonanza, an especially rich vein of a precious ore.

Terry Tempest Williams