The Gravity Borax Method (GBM) of Sustainable Au Ore Processing


The Gravity Borax Method (“enhanced gravimetric method” or “Filipino method”) for sustainable Au recovery employs gravity, and a sluice box lined with balleta's (wool carpets) used to concentrate the Au from the milled or crushed slurry which is then collected in a pail, finely ground and panned using soap to concentrate the Au-ore which then is mixed with eco-friendly low-cost borax, and smelted in a crucible between 1150 – 1450 Celsius to separate the minerals to recover the Au leaving only a slag.


The GBM was developed by AS miners in Benguet, Philippines on the island of Luzon in the 1900’s, and more recently introduced to ASG miners by Scientists conducting Hg-amalgamation vs. the GBM competitions, and is used collectively by approximately 30,000 ASG miners in Bolivia, Philippines, Tanzania, Indonesia, Zimbabwe, Sudan Africa, and Kenya consistently reporting 3 (three) times more Au safely recovered, and up to 5 (five) times more Au recovered by miners in Bolivia without producing toxic tailings wastes providing these miners incentive to immediately switch from using Hg.


This is happening today in Bolivia.


The Material Safety Data Sheet lists Borax® (Sodium Tetraborate, Decahydrate (Na2B4O7.10H2O)) as a health hazard of 1, the same as baking soda and salt. Borax is classified as non-carcinogenic, a mild skin irritant. 


Personal protection: Where airborne concentrations are expected to exceed exposure limits, NIOSH/MSHA certified respirators should be used.

"Eye goggles and gloves are not required for normal industrial exposures, but may be warranted if environment is excessively dusty."


According to The U.S. Department of Agriculture (USDA), "The use of Sporax® (borax) in the control of annosum root disease does not present a significant risk to humans or wildlife species under most conditions of normal use, even under the highest application rate".

Studies in China

Owing to the geological situation, high boron exposures are reported in parts of Northeast China, and are related to environmental, lifestyle and occupational factors (Chang et al. 2006).


Scially et al. (2010) compiled studies on nearly 1000 men and women in boron mining or processing in the Liaoning province of China. These included individual assessments of boron exposure, interviews on reproductive experience and data on semen analysis. Employed men living in the same community and in a remote community were used as controls.

"No compelling evidence of male reproductive effects attributable to boron could be obtained in highly exposed workers. This was supplemented by a further study of possible interactions of occupational boron exposures and semen quality that again found no significant correlations between blood or urine boron concentrations and adverse semen parameters (Robbins et al. 2010)".

The Journal of Health Pollution published research that proved more than twice as much, and up to 5 times more Au was recovered from milled ore using Borax as a flux for smelting than using mercury amalgamation, and without need of investment in new processing equipment, and up to 30% faster.

Borax is a component of many detergentscosmetics, and enamel glazes. It is used to make buffer solutions in biochemistry, as a fire retardant, as an antifungal compound, in the manufacture of fiberglass, as a flux in metallurgy, neutron-capture shields for radioactive sources, a texturing agent in cooking, as a precursor for other boron compounds, and along with its inverse, boric acid, is useful as an insecticide.

According to Appel and Na-Oy (2012) Gold extraction using borax for ASG miners has been successfully tested and operational in the Philippines, Indonesia, Tanzania, Bolivia, and Zimbabwe for decades, and approximately 15,000 ASG miners in a small area of Luzon, the main island in the northern portion of the Philippines, use this method exclusively reporting as much as 3 times Au recovery than mercury. 

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