Silver was originally discovered by Spanish explorers at La Luz in 1548, and subsequently at Guanajuato in 1552. Guanajuato is considered to be one of the top three historic silver mining districts in Mexico, having produced an estimated 1 to 1.2 billion oz silver and 5 to 6 million oz gold. At their peak during the 1700's, the silver mines of Guanajuato and La Luz were thought to be the largest and richest silver mines in the world.
Industrias Penoles SA de CV ("Penoles"), one of Mexico's largest industrial and mining conglomerates, developed the Bolañitos and Las Torres mines and plants in the La Luz and Guanajuato districts respectively in the 1970's.
When the price of silver bottomed after 2000, Penoles leased many of its smaller silver mining operations to local mining companies.
The Veta Madre and La Luz veins are classic, low sulfidation epithermal vein systems. Mineralization consists of disseminations and fracture-fillings of pyrite, pyrargygrite, polybasite and electrum in quartz-calcite veins ranging from 1 to 30 metres thick but averaging 2 to 3 m wide. Multiple historic ore zones (now stopes) formed steep-plunging shoots 100 to 500 m long that were mined down to depths of 200 to 600 m. More than 30 shafts were driven historically into the two vein systems on the Bolañitos and Cebada properties, of which five are still active.