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A second metal changes the equation
Anyone following drill results from established gold belts will occasionally encounter announcements reporting not only gold grades but also substantial antimony. What sounds like an incidental finding can significantly alter a project’s economics. Antimony (Sb) appears on the EU’s and the United States’ lists of critical raw materials because it is needed for flame retardants and semiconductor manufacturing, and rising demand from new energy-storage technologies is adding further pressure on a supply chain that was already stretched. Its natural co-occurrence with certain gold deposits has given specific exploration areas a strategic dimension that drew almost no attention a few years ago.
For newcomers to junior miners, this matters for a straightforward reason: the valuation logic of a project with two marketable metals differs from that of a pure gold discovery. Without grasping this, investors either miss the added value or are misled by impressive-looking metrics built on shaky assumptions.
Antimony: scarce supply, growing demand
Antimony is produced in meaningful volumes at only a handful of locations worldwide. China has historically dominated, at times accounting for more than 50 percent of global output. That concentration has sparked geopolitical debate: when one state controls nearly the entire supply, the dependencies that follow have led the European Commission and the U.S. Department of the Interior to classify antimony as a supply-security risk in their respective strategies.
Demand, meanwhile, is rising. Antimony is used as an alloying metal in lead-acid batteries, plays a role in photovoltaic manufacturing, and is attracting interest in sodium-antimony battery development. For explorers who can demonstrate antimony as a by-product of a gold project, that supply-demand imbalance creates an additional revenue line — one that could matter or could evaporate depending on where prices go.
What AuEq actually tells you
When a company reports a drill intersection as a gold-equivalent value (AuEq), it converts different metal grades into a single number. The arithmetic is simple; the assumptions packed inside are not.
The base formula: AuEq = gold grade + (antimony grade × antimony price / gold price). The higher the antimony price relative to gold, the more a tonne of antimony mineralization lifts the reported equivalent. If that price ratio shifts — which happens routinely in commodity markets — all published AuEq figures change their economic meaning, even though the rock itself is unchanged.
Consider a core intersection grading 5 g/t gold and 2% antimony. At USD 3,000 per ounce of gold and USD 25,000 per tonne of antimony, the AuEq is one number; at USD 10,000 per tonne of antimony it is a substantially lower one. Same drill hole, different story. The footnotes in any announcement are where the real reading starts.
| Factor | Impact on AuEq value |
|---|---|
| Rising antimony price | Increases AuEq at unchanged grades |
| Falling gold price | Increases the relative Sb contribution to AuEq |
| Metallurgical separability | Determines whether both metals can actually be recovered |
| Regulatory approval | Antimony processing is sometimes subject to additional permitting requirements |
| Offtake agreement | Often absent in early-stage exploration |
Where co-production gets complicated
The economic case for a two-metal project is real, but it has a flip side. A pure gold project turns on a handful of variables: grade, tonnage, recovery rate, gold price. Add antimony and you double the price risk exposure, and on top of that comes the metallurgical question of whether the two metals can actually be separated at a cost that makes sense.
Antimony typically occurs as stibnite (Sb₂S₃), a sulfide mineral that sits in close spatial association with gold-bearing quartz. That geological proximity is why high-grade antimony zones tend to show up in exactly the same locations as peak gold values. For processing, this creates a choice: smelt the ores together and risk mutual interference, or add separation stages that cost money no one can reliably estimate during early exploration. Neither path is cheap, and neither is well understood until metallurgical test work is done.
There is also a distinction that gets glossed over in many announcements. Under the Canadian NI 43-101 standard, Resources (Inferred, Indicated, or Measured) are geological estimates without confirmed economic viability. Reserves (Proven or Probable) are permitted, economically demonstrated extraction volumes. Drill results from ongoing programs produce Resources, not Reserves. The difference is not semantic — it determines whether the tonnage on the page could ever become a mine.
Reading antimony-gold projects without getting misled
The growing number of drilling programs reporting significant antimony alongside gold reflects changed market conditions, not a sudden geological discovery. What was once treated as a nuisance contaminant now draws attention because of where antimony sits in the supply-chain debate. That attention is not misplaced, but it can run ahead of the facts on the ground.
The questions worth asking are specific. Which metal prices feed the AuEq calculation, and do they reflect current market conditions? Are there metallurgical test results showing that separation is viable at those costs? Do the reported grades come from individual drill intervals or classified resources? And who actually buys antimony in the relevant jurisdiction, because the pool of antimony buyers is far smaller than the market for gold. A project that cannot answer those questions clearly is asking investors to carry more uncertainty than the headline numbers suggest.
Key terms explained
- AuEq (gold equivalent)
- A metric that converts various metal grades into a unified gold value based on their respective market prices. Enables comparison across different ore bodies, but requires stable price assumptions.
- Critical raw material
- A metal or mineral classified by governments (EU, U.S., and others) as both economically significant and subject to supply risk. Inclusion on such a list raises political interest but guarantees neither prices nor offtake.
- Stibnite (Sb₂S₃)
- The most common antimony mineral, chemically antimony sulfide. Frequently occurs alongside gold-bearing quartz zones in epithermal and mesothermal gold systems.
- Resources vs. reserves (NI 43-101)
- Resources (Inferred / Indicated / Measured) are geological estimates without confirmed economic viability. Reserves (Proven / Probable) are permitted, economically demonstrated extraction volumes. The two terms must not be used interchangeably.
- Metallurgical separability
- The technical ability to economically separate two or more metals from a shared ore body. Determines whether a co-production project is workable in practice.
- Co-production
- A mining concept in which two or more metals are extracted simultaneously from the same ore body. Increases potential revenues but also raises metallurgical and commercial complexity.
- Offtake agreement
- A contract between a producer and a buyer securing the purchase of a defined production volume under agreed terms. Particularly relevant for co-production projects, as antimony buyers are far fewer in number than gold buyers.
⚠️ Important notice: This article is for informational and educational purposes only. It does not constitute investment advice, a recommendation, or a solicitation to buy or sell any security. Investments in small-cap exploration and mining companies carry a high risk, including the potential total loss of capital. Before making any investment decision, consult a registered financial advisor and conduct your own analysis. Boersen Post Team is not responsible for decisions taken based on the content published here.
