Almaden Quicksilver

 



El Casa Grande

While moored at Brisbane Marina, we rented a car and drove to the town of New Almaden to visit El Casa Grande.  This grand house, once a residence for a succession of mine managers and their families, is now the home of the New Almaden Quicksilver Mining Museum.  Dedicated to the history, geology, and mining communities of New Almaden, the museum provides a glimpse of life in Santa Clara County 150 years ago. 






Beautiful Rooms in the Casa

Rooms of the home display period furniture and artifacts of daily living, while another portion of the home depicts the region’s mining history through photographs taken by a doctor who witnessed one of the world’s largest mercury-mining operations of its time.  Mining operations in New Almaden first began in 1845 under the claim of Mexican Cavalry officer Captain Andres Castillero.  Castillero discovered that the red rock was cinnabar, an ore containing mercury.  Considered a valuable commodity, mercury was needed to process silver in Mexican silver mines and later to process gold discovered in California.  Mercury, also called “quicksilver” is still used in levels, thermometers, lamps, barometers, batteries, electronics, medicine, and agriculture.  

Cinnabar

The red rock harvested from the hills of New Almaden spawned a thriving economy and several settlements in the area.  American companies eventually acquired ownership of the mines, where operations continued under the management of Captain Henry Halleck.  Halleck had the Casa Grande designed and built in 1854, which served as the official residence and office of a succession of mine superintendents for several decades and was also used as a weekend retreat for wealthy mine investors. 

Efficient Processing with Furnaces

The earliest processing of cinnabar ore at New Almaden was done by heating the ore in huge metal “whale pots” to extract the mercury, a crude but effective method due to the richness of the ore (sometimes more than 60 percent mercury).  After the richest ore was depleted, the ore had to be roasted to recover the same amount of mercury from far greater quantities of low-grade ore.  Small batches of mercury could be extracted by using a retort, a device similar to a moonshiner’s still.  Large furnaces and condensers improved and evolved so more mercury could be recovered from each ton of ore; however, the furnaces had to be cooled periodically and cleaned out before starting another batch – a time-consuming, labor intensive process.  An experimental furnace, constructed at New Almaden in 1874, revolutionized ore processing.  This new reduction process allowed ore to slowly trickle into the top of the furnace.  Gravity then brought the ore slowly down a vertical shaft and out the bottom while its mercury content was vaporized, condensed, and collected.  

Filling Iron Flasks with Mercury

During the late 1870’s, New Almaden produced more mercury than any other mine in the world.  The New Almaden Mine produced 83,974,076 pounds of mercury until the operations ceased in 1976.  Long after innovative methods of processing ore became available, miners at New Almaden continued to use primitive methods to obtain the ore – blasting with black powder and drilling holes by hand with one-inch steel bits.  More than 50 miles of tunnels honeycomb the hills of New Almaden, nearly all were built by hand.  

Cinnabar Ore Mine Shaft

Stacks of Wood Beams used for the Tunnels 

The mine property and the Casa Grande make up the Almaden Quicksilver County Park with miles of trails, remnants from the past, and informative plaques describing the communities of Mexican, English, and Chinese miners and their families.

Cinnabar Paste Used for Design



Red Dots show Cinnabar located around the World