Resource Growth Is Priced In, Not Drilled

Canterra Minerals' Lundberg deposit in Newfoundland got bigger this year, at least on paper. The company's table shows Indicated tonnage up 55%. Contained copper rose only 34%, because the rock got thinner. MINING.COM reported that Lundberg's indicated copper-equivalent grade fell 13% from 1% in the 2019 resource.

That gap between tonnage and metal is the story. Across copper and gold, resource updates now routinely lead with a tonnage jump that owes much to the metal-price assumption underneath it. A higher price lowers the cut-off, pulls marginal rock into the pit shell and inflates the headline. The deposit has not necessarily improved. The ruler has changed.

Three updates, one pattern

Start with Lundberg. Canterra says the Indicated category now holds 26.1 million tonnes, against 16.8 Mt in the 2019 estimate. It credits 4,779 m of drilling since it acquired the project in 2024, together with an optimized pit shell at updated metal prices. The earlier estimate, filed in 2024, used US$3.00/lb copper and US$1,250/oz gold. MINING.COM reported that the new shell reflects much higher price assumptions than the old one. Drilling is real, then, but so is the price effect, and the release does not say how much each contributed.

Canterra itself is careful about what the shell means. Its release says "The shells are resource reporting constraints, not proposed mine plans." The company is also shifting attention to the higher-grade Two Level zone, where the Inferred resource of 0.87 Mt grades 1.54% CuEq. When a company's own next step is to chase better rock, the bigger low-grade block is not the prize.

Selkirk Copper is more explicit. Its Minto update in the Yukon, announced July 30, 2026, reports Measured and Indicated resources of 47.8 million tonnes, a 280% increase in tonnage on the 2025 estimate. The company says updated pricing and design assumptions pushed lower-grade material above the cut-off, lifting tonnage and lowering average grade. Its own evaluation divides the Indicated expansion between price and design-basis changes on one side and exploration success through drilling on the other. Selkirk's deck assumes USD$4.60/lb copper and USD$3300/oz gold. Its release lists "metal price assumptions" among the factors that may affect the estimate. The Minto open-pit resource of 21.8 million tonnes grades 0.59% Cu. The underground portion, at 26.0 million tonnes, grades 1.14%.

IAMGOLD's Côté Gold shows the same mechanics in gold. The company reported on June 1, 2026 that Measured and Indicated resources reached 20.3 million ounces, up 12% on the Dec. 31, 2025 statement. It said the rise was primarily driven by a higher gold-price assumption for the Côté zone, from $2,100/oz to $2,500/oz, plus ounces from a consolidated block model. The cut-off fell to 0.25 g/t from 0.30 g/t. The variance table shows tonnes up 22%, grade down 8% and ounces up 12%. More rock, thinner rock, a bigger number.

Why the price deck keeps rising

None of this is sleight of hand. Prices did rise, and the copper market is where the assumptions come from. Bloomberg News reported on September 7, 2026 that three-month LME copper gained as much as 0.8% to $14,533 a ton, beating the previous record set in January. Bloomberg added that the record came "even in a tepid environment for demand," with stockpiles heavily concentrated in the US. Market data show the COPX copper-miners ETF climbing from $59.81 in September 2025 to $86.28 so far in October.

The supply side explains why miners reach for lower-grade rock. S&P Global's January study, "Copper in the Age of AI," projects a supply deficit of 10 million metric tons by 2040. It cites declining ore grades and rising energy, labor and input costs, and says a new mine takes 17 years on average from discovery to production. Bloomberg reported that the world's ageing big mines are struggling to keep pace with demand from data centers, renewables and grids. Chile's copper shipments, it added, sank to the lowest in more than a year in August despite surging prices. With few big, rich discoveries, re-measuring known deposits at higher prices is one way to add tonnes.

The fair objection

The obvious defense is that economics define a resource. If copper pays, the marginal rock is a legitimate target, and pit shells should move with prices. Atrium Research analysts Riley Venton and Nicholas Cortellucci said, in comments MINING.COM reported, "The higher-confidence resource confirms Lundberg as a large open pit copper-zinc resource at a brownfields past-producing site." MINING.COM also reported that Canterra shares gained 4% to 13¢ and that Atrium raised its target to 35¢ from 30¢. Investors are paying for the bigger number, and some of it is earned: Selkirk's own split credits drilling for part of the gain.

But that defense concedes the point. A resource that grows with the price can shrink with it, and it says little about whether anyone can build a mine. MINING.COM reported on Monday that front-month gold settled at $4,345.80, about 18% below its January record of $5,318.40, and that with bullion no longer lifting every gold stock, acquisitions, mine builds and financing decisions will have to stand up on their own merits. Merit means grade, strip ratio, capital and permits. None of those appear in a headline percentage.

What follows

Readers should treat the price assumption as the first line of any resource release, and look next at grade and contained metal. Contained metal is the honest measure of what drilling found. At Lundberg it rose 34%, not 55%. Companies that report both, and say how much of the gain is geology, deserve credit. Selkirk did. Not every issuer will.

The next test is already scheduled. IAMGOLD says its Côté estimate will inform a technical report and mine plan in the fourth quarter of 2026 evaluating a plant expansion. A mine plan has to pay for every tonne it digs, so it shows how many of the new ounces are ore and how many are only a price assumption.