RTB Boron is an open pit borate mining operation located within the Kramer Borate deposit in Boron, California.

The Kramer ore body is a roughly lenticular sedimentary sequence of borax (Na2B4O7.10H2O) and kernite (Na2B4O7.4H2O) containing interbedded claystone. This central crystalline facies is successively enveloped by facies consisting of ulexite (NaCaB5O9.8H2O) and colemanite (Ca2B6O11.5H2O) - bearing claystone, and barren claystone. Studies indicate the Kramer borates were deposited in a small structural, non-marine basin, associated with thermal (volcanic) spring activity during Miocene time.

The Miocene Kramer beds are divided into three distinct members, the Saddleback basalt member, the Shale member, and the Arkose member, in ascending order. The Saddleback basalt comprises up to 600 feet of olivine basalt flows and is the only Kramer member forming surface outcrops – as ridges northwest, north, and northwest of Boron open pit. The basalt is overlain by the Shale member, which consist of up to 400 feet of borate-bearing and barren claystones and shale. The Shale member is overlain by the Arkose member, which comprises up to 800 feet of arkosic sandstones, which are locally silty and interbedded with tuffaceous clays.

The sodium borate facies is divided into seven stratigraphic units:

- Four high-grade units: Upper ore, Middle ore, Lower ore, and Basal ore, typically contain over 75-percent borax.
- Three generally low ........

Boron is a largest open pit mine in California and one of the richest borate deposits on the planet. The mine has been in operation since 1923. Firs, as an undeground mine and later as the open pit. Current 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.

Boron Operation consists of the open pit mine, an ore crushing and conveying system, 2 process plants (Primary Process and Boric Acid Plant), Shipping facility, and tailings storage facilities.

The current mining method is conventional truck and shovel, mining at appropriate bench heights. Current mining practices include grade control utilizing blast hole data.

The ore mining equipment (wheel loaders occasionally assisted by dozers or backhoes for additional separation) is smaller than the waste shovel fleet to facilitate better selectivity duringmining. The SMU is at smallest a 5 foot cube, representing sand backfill in old underground workings, which is incorporated into the block model. Mining practice in the stope areas involves using the backhoe or dozer to remove backfill from the stopes ahead of ore mining, minimizing dilution and ore loss.

Sodium borate mining recovery for open pit mining in Boron is estimated at 95% for the life of the mine. Calcium borate recovery is estimated at 60% for open pit mining, and 95% for stockpile mining.

Dilution is not factored into reserve calculations because B2O3 tons are no ........

- subscription is required.