Antimony by-product material is popping up all over the world and as junior miners look to advance gold projects.

Geologically related to lode gold deposits

The principal ore mineral of antimony is stibnite (Sb2S3), which gives the element its chemical symbol. Over 80% of the world’s antimony is produced from carbonate replacement deposits and gold-antimony epithermal vein-hosted deposits, with China being the largest producer, from primary antimony mines.

Chinese mine supply has been declining, spurred on by increasingly exhausted reserves and lower ore grades. This has led to the country turning to imported antimony ores to feed the world’s dominant antimony ingot supply chain. Traditional large antimony sources outside China are mercury-antimony deposits in Tajikistan and Kyrgyzstan. However, as China started to increase demand for imported stibnite, increasing volumes emerged from mixed gold-antimony concentrates. It turns out that stibnite is commonly associated with vein-hosted gold deposits.

One mine floods the market

Gold is one of the most traditionally mined commodities, but large open pit and underground deposits have been challenged by increasing volumes of low-grade heap-leaching recovered gold – with lower costs. By-product credits are a good method to improve economics. Between 2010 and 2015, antimony ingot prices were at over US$8,000/t and after a short trough returned to this level in end-2017.

Over this period gold prices had declined to between US$1,200-1,300/oz and margins were tighter. Polyus in Russia, one of the top-5 gold miners globally, instantly became the world’s largest antimony mine producer, when the company started to sell by-product gold-rich antimony flotation concentrates from its Olimpiada mine. Polyus flooded the market with the addition of 23kt Sb and, while not all smelters in China were able to process the concentrates from Polyus, the supply from Olimpiada maintained a surplus market over 2018 and 2019, which drove prices back down to the 2016 floor by H2 2019.

The company continued to sell gold-rich antimony concentrates over 2020, but with gold prices returning to above US$1,800/oz the antimony tap from Olimpiada ran dry, with antimony revenues (even at 100% value) less than 1% of metals recovered from Olimpiada. Now with smelters invested to consume these new types of ores, the market has returned to a marked deficit and prices increased.

What to expect

Antimony by-product material is popping up all over the world and as junior miners look to advance gold projects, many are dipping their toes into the antimony market as a potential by-product upside. However, with Polyus capable of instantly restarting over 10% of global antimony requirements the risk for new players remains high. In the near term, a new gold mine in Tajikistan owned by Talco Gold – a JV between Talco and Chinese Huayu – is set to provide as much as 16ktpy of contained antimony. But these volumes will also be dependent on the gold market.

In the meantime, secondary antimony from recycled lead-acid batteries (antimonial lead) is moving into surplus as electric vehicles and lithium-ion batteries are dampening growth for traditional batteries, which themselves are switching to lower antimony loadings in favour of tin-based valve-regulated lead-acid (VRLA) batteries. This could provide a further source of growing antimony available for the market, however, the economics of converting antimonial lead into high-purity antimony trioxide (ATO) used in plastics and flame retardants is still challenging. Nevertheless, Project Blue forecasts a significant surplus of antimonial lead to be available over the energy transition period and Chinese lead smelters have already started supplying low-grade ATO to the market.