Boron, California Operations

Meeting a third of the world’s refined boron demands

U.S. Borax operates California’s largest open pit mine in Boron, California—one of the richest borate deposits on the planet. While boron is present everywhere in the environment, substantial deposits of borates are relatively rare. We're finding better ways to provide the materials the world needs by supplying around one-third of the world’s demand for refined borates. Our operations are designed to create high-quality products to meet global needs for boron.

Mining and Refining

We produce approximately 1 million tons of refined borate ore every year from our boron mine. It produces about a third of the world's supply of refined borate products.

The mine measures 1.74 miles (2.8 km) wide, 1.99 miles (3.2 km) long, and is up to 755 feet (230 m) deep. More than 80 minerals are found at this geologically unique site, including the four boron-based minerals in greatest demand by industry: Tincal, kernite, ulexite, and colemanite.

Our processing plants produce products such as borax pentahydrate, borax decahydrate, and boric acid. Our fusing plants also produce anhydrous borate products. Each of our sites is ISO 14001 certified.

Mining and refining are age-old activities. Yet, U.S. Borax continually improves practices to raise productivity, ensure the safety of our team, and minimize our environmental impact. At each stage of the process, borate samples are tested at on-site laboratories, enabling instant analysis and adjustments.

Mining borates relies primarily on a combination of drilling, blasting, and shoveling to collect ore, which is then hauled to massive crushing machines. From there, it is transported to refinery centers.

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Drilling and Blasting

Drilling is an important part of exploration, and it is the best way to sample the type and purity of ore beneath the ground. Information about the deposit's location and composition is fed into a computer to develop long-term mine plans. Drills are also used to dig blast holes.

Explosives are used to blast loose the sandstone (called overburden) at the top of the deposit and to loosen the boron ore below it.

Drilling and blasting at the mine

Shoveling and Hauling

Once the ore and overburden are loosened, enormous shovels scoop up the rubble from the bottom of the mine and dump it into haul trucks that can carry 220 tons (199.6 metric tons) each.

Ore from the mine must be crushed before it can be refined. Powerful crusher machines reduce the ore to 1-inch (2.5 cm) pieces, increasing the ore's surface area to make the refining process more efficient.

Ore is transported out of the mine and throughout the refinery via an extensive system of conveyors.

Hauling boron


Six primary steps are required to refine raw ore into refined borates. The bulk of this process was developed at our Boron Operations:

  • Dissolving: Crushed ore is mixed with hot liquor—a combination of borates and water. The borates dissolve in the water. Insoluble rocks, sand, and other solids are removed using screens.
  • Settling: The saturated borate solution is pumped into large settling tanks, called thickeners. Heavier clay settles to the bottom of the tank, leaving the liquor on top.
  • Crystallizing: The liquor is transported to tanks, called crystallizers, to be cooled. The drop in temperature forces the borates to crystallize, forming a slurry of borate crystals and water.
  • Filtering: The slurry is poured over special fabric filters and washed to ensure purity. Water is drawn away by a vacuum beneath the filter.
  • Drying: Damp borate crystals are then transferred to huge rotating dryers that use hot air to finish the crystal drying process.
  • Conveying: Dry borates drop onto a conveyor belt to be transported for storage or packaging and shipping.

Refining boron

Testing and Storing

At each stage of the process, borate samples are taken for quality checks. Our onsite laboratories enable instant analyses and adjustments.

We store refined borates in silos or the 18,000-ton (16329-metric ton) domes at Boron Operations. Total storage capacity at the site is more than 90,000 tons (81,647 metric tons).

Learn more about our testing methods.

Storage domes at Boron, California

Our Location

14486 Borax Road
Boron, CA 93516 USA
+1 760 762 7000
Jen Brown, Communication and Media for Operations
Boron Operations Map

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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