Acanthite with Arsenopyrite (G-030)

specimen number:
9273049

location:
La Valenciana Mine, Guanajuato, Mexico

description:
A neat ore sample for this famous locality with masses and veins of metallic acanthite across matrix with arsenopyrite.

The La Valenciana mine is located just north of Guanajuato, Mexico, and ranks historically as one of the most prolific silver producers in the world. Geologically, the deposit sits directly along the Veta Madre (Mother Vein), a massive northwest-trending, low-sulfidation epithermal vein system that extends for roughly 25 kilometers and cuts through a complex sequence of Mesozoic sedimentary and Tertiary volcanic rocks. The economic silver and gold mineralization occurred about 30 million years ago when boiling hydrothermal fluids deposited precious metals alongside quartz, calcite, and the distinct local potassium feldspar variety known as valencianite. Spanish explorers initially opened a shallow mine at the site in 1557, but it was quickly abandoned in 1568 due to technological limitations. The modern history of the site truly began in 1750 when a massive, high-grade silver vein was rediscovered, leading to full-scale commercial operations starting in 1760 under Don Antonio de Obregon y Alcocer. By the late eighteenth century, the mine was the crown jewel of New Spain, single-handedly producing roughly twenty to thirty percent of the entire global silver output. Deep vertical shafts, including the massive octagon-shaped San Jose shaft, eventually reached depths exceeding 600 meters to extract sulfide ores. Industrial corporate mining continued through the nineteenth and twentieth centuries, navigating interruptions from the Mexican War of Independence and subsequent structural changes. Remarkably, while parts of the property have transitioned into a popular historical show-mine museum, sections of the Valenciana complex continue to see active, modern underground mining and exploration operations today.

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