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:
o Four high-grade units: Upper ore, Middle ore, Lower ore, and Basal ore, typically contain over 75-percent borax.
o Three generally low-grade units, A-zone, B-zone, and C-zone, which typically contain less than 60-percent borax.
o The Basal ore is the thinnest and least extensive of the high-grade units; the Lower ore is the thickest and most extensive highgrade unit. Only in the thick central portion of the sodium borate facies, are all the units present. Stratigraphic control is maintained by use of a number of clay-tuff and claystone marker beds within the sodium borate facies.

The current mining method is conventional truck and shovel, open pit 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 not affected by diluting materials. However dilution is included in mining schedules. The effect of dilution is to increase the crude tons of material into the process plants, thereby reducing the ore grade and slightly elevating costs. Typical dilution rates applied are 10% for tincal mined and 3% for kernite mined.

Dilutants primarily include hanging- and footwall ulexite, and to a lesser extent different wastes directly in contact with ore at fault contacts. This is referred to as “contact dilution”. Secondarily, the sand used historically to backfill underground stopes is called “stope dilution”. Contact and stope dilution are calculated in the mining schedule, since modelling these directly in the block model would be exceedingly complex, and dilution is variable depending on location and separation ability.

The Primary Process plant uses the MDDK process to dissolve the ore. MDDK involves the fine grinding of a blend of tincal and kernite ores followed by dissolution in water in a series of agitated tanks. A mechanical evaporator is added to the sodium borate process to allow direct usage of MDDK-derived liquors for both sodium borate pentahydrate (Neobor) production and sodium borate decahydrate (Borax) production. The Boric Acid Plant uses sulfuric acid to dissolve kernite due to the relatively slow water-solubility of kernite ore. After dissolution, the gangue is separated using rake classifiers, and the liquor is sent to thickeners for settling of fine clays.

Boron ore is principally composed of three main components: borate, clay, and water, with minor amounts of deleterious materials present locally. Deleterious materials are blended in the feed to maintain manageable concentrations.

RTB Boron has been in operation for over 90 years, as such, the process techno ........