Mother lode

Mother lode is a principal vein or zone of veins of gold or silver ore. The term is also used metaphorically to refer to the origin of something valuable or in great abundance.

The term probably came from a literal translation of the Spanish veta madre, a term common in old Mexican mining. Veta madre, for instance, is the name given to an 11-kilometre-long (6.8 mi) silver vein discovered in 1548 in Guanajuato, New Spain (modern-day Mexico).

In the United States, Mother Lode is most famously the name given to a long alignment of hard-rock gold deposits stretching northwest to southeast in the Sierra Nevada of California. It was discovered in the early 1850s, during the California gold rush. The California Mother Lode is a zone from 1.5 to 6 kilometres (0.93 to 3.73 mi) wide and 190 kilometres (120 mi) long, extending from Georgetown in El Dorado County on the north, through Amador, Calaveras, and Tuolumne counties, south to Mormon Bar in Mariposa County.

Following the elucidation of the theory of plate tectonics, the Mother Lode was found to coincide with the suture line of a terrane, the Smartville Block. The zone contains hundreds of mines and prospects, including some of the best-known historic mines of the gold-rush era. Individual gold deposits within the Mother Lode are gold-bearing quartz veins up to 15 metres (49 ft) thick and a few thousand feet long. The California Mother Lode was one of the most productive gold-producing districts in the United States. Now it is known as a destination for tourism and vineyards.

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