Electrum (G-029)

specimen number:
9273167

location:
La Valenciana Mine, Guanajuato, Mexico

description:
A thin loose delicate wire of electrum held together with crystallized calcite and coming off matrix.

The La Valenciana mine, situated on the northern edge of Guanajuato, Mexico, was one of the most prolific silver-gold mines in global history. Geologically, the deposit is hosted along the Variscan-age Veta Madre (Mother Lode), a major northwest-trending epithermal fault vein system that cuts through Mesozoic metamorphic rocks and Tertiary volcanic sequences. Hydrothermal activity along this fault deposited rich bands of argentite, polybasite, electrum, and native silver within a gangue of quartz and calcite. Formal exploration began in 1760 under Antonio de Obregon y Alcocer, and by 1768, the operation struck a massive bonanza zone, leading to the construction of the iconic Octagonal Shaft (Tiro General). The mine operated continuously at extraordinary capacity through the late eighteenth century, producing a significant percentage of the world's silver, until the Mexican War of Independence disrupted production in 1810. Following periods of flooding and intermittent exploitation by British and American consortia in the nineteenth and twentieth centuries, the mine underwent cooperative local management before transitioning into a protected historic and tourist destination, though localized mining exploration persists in the region today.

Electrum is a naturally occurring alloy composed primarily of gold and silver, often containing trace amounts of copper, iron, and other metals. It crystallizes in the isometric system, typically appearing as dendritic growths, thin flakes, or microcrystalline grains within hydrothermal vein systems rather than distinct, well-formed crystals. The color of electrum ranges from a pale brassy yellow to a brilliant silvery gold, depending strictly on the percentage of silver present, which generally fluctuates between twenty and fifty percent. Geologically, it serves as a key ore mineral in low- to intermediate-sulfidation epithermal deposits, where it precipitates alongside base-metal sulfides and quartz. Valued since antiquity, electrum was used to mint the very first metal coins in Lydia during the seventh century BC, and it remains a highly prized target for modern precious-metal mining operations worldwide.

Questions about this specimen?
Send an email or call us: 314-341-1811.