The remains of mercury mines, which were created during the time of Francisco Pizzaro, can still be seen outside of Huancavelica on the mercury mine hike. A three-hour round trip hike leads to the village of Santa Barbara and the remains of the mercury mines, which were closed in the mid 1970s. The entrance to the original mine can still be seen past Santa Barbara on the way to the mining installations. The entrance is not sealed off but entering the old mercury mine is not recommended for safety reasons. The mine is nicknamed Mina de la Muerte, meaning death mine. Some of the locals still mine mercury on a small scale.
From Wiki.
The area was the most prolific source of mercury in Spanish America, and as such was vital to the mining operations of the Spanish colonial era. Mercury was necessary to extract silver from the ores produced in the silver mines of Peru, as well as those of Potosí in Perú superior ("Upper Peru," now Bolivia), using amalgamation processes such as the patio process or pan amalgamation. Mercury was so essential that mercury consumption was the basis upon which the tax on precious metals, known as the quinto real ("royal fifth"), was levied.
The extraction of the quicksilver in the socavones (tunnels) was extremely difficult. Every day before the miners came down, a mass for the dead was celebrated. Due to the need of numerous hand-workers and the high rate of mortality, the Viceroy of Perù Francisco de Toledo resumed and improved the pre-columbian mandatory service of the mita. Despite the risks, the mining attracted people from all over the Viceroyalty. The alloted concession were rectangular, about 67x33m. Miners were divided in carreteros and barreteros.
In 1648 the Viceroy of Peru, declared that Potosí and Huancavelica were "the two pillars that support this kingdom and that of Spain." Moreover, the viceroy thought that Spain could, if necessary, dispense with the silver from Potosí, but it could not dispense with the mercury from Huancavelica.