Altamira Gold’s Maria Bonita Resource Jumps 82% to 1.31 Moz

Just 3,868 metres of drilling added roughly 590,000 ounces of gold. That single ratio, close to 150-155 ounces of new resource for every metre drilled, is the story behind Altamira Gold’s latest resource update, and it is the kind of efficiency that separates one style of gold deposit from all the others.

The numbers arrive at a moment when two forces are pulling in the same direction. The Maria Bonita deposit in Brazil is a porphyry-hosted gold system where mineralisation runs almost continuously through the rock, so nearly every metre of the drill bit intersects economic-grade material. And gold near US$4,150-US$4,300/oz makes low-grade, high-tonnage ore economically compelling in a way it simply was not when the project was first assessed in 2019 at US$1,500/oz.

What follows here is a look at whether the resource growth at Maria Bonita is geologically and economically substantive, or whether the headline figures mask risks that should temper the enthusiasm. Here is how to read the update, the geology driving it, the gold price doing much of the heavy lifting, and the milestones that will decide what happens next.

From 720,000 to 1.31 million ounces: what the September 2026 resource update actually shows

On 21 September 2026, Altamira Gold announced a substantial increase in the mineral resource at Maria Bonita, with an effective date of 16 September 2026. The updated open-pit estimate now stands at approximately 1.31 million ounces of contained gold.

Break that into its two categories and the shape of the growth becomes clear. Indicated resources rose to 25.0 Mt at 0.50 g/t Au for 403,877 oz, up from the maiden estimate of 24.19 Mt at 0.46 g/t for 357,800 oz. Inferred resources, by contrast, jumped to 70.0 Mt at 0.41 g/t Au for 908,477 oz, from a maiden base of just 25.64 Mt at 0.44 g/t for 362,400 oz.

That is the number that matters. Indicated ounces grew modestly, while Inferred ounces nearly tripled. The bulk of the headline growth sits in the lowest-confidence category of the resource, which means much of what Altamira has added represents geological potential rather than value you can take to a bank today.

The cut-off grade also shifted, from 0.20 g/t to 0.24 g/t Au. A cut-off grade is the minimum concentration of gold that makes a block of rock worth mining. The move higher signals a revised economic framework underpinning the estimate, one built on a higher assumed gold price and a larger optimised pit.

The higher-grade core within the resource

Within that broad, low-grade envelope sits a denser core. Applying a 0.5 g/t Au cut-off isolates a higher-grade subset: Indicated of 9.30 Mt at 0.75 g/t for 225,630 oz, and Inferred of 11.11 Mt at 0.80 g/t for 286,859 oz.

This is the material that carries the most weight for any future mine plan. It is higher confidence and higher value, and it would sit at the heart of the early years of production if the project ever advances that far.

Why 3,868 metres produced 590,000 ounces: the geology behind the efficiency

To understand why the drilling was so productive, start with what kind of deposit this is. Maria Bonita is a porphyry-hosted gold system, meaning the gold is spread broadly and continuously through a large body of intrusive rock rather than concentrated in narrow, discrete veins.

The mechanical reason each metre of drilling at Maria Bonita intersects economic-grade material is rooted in porphyry deposit geology, where large intrusive bodies distribute metals broadly and continuously through the host rock rather than concentrating them in narrow, intersectable veins.

That distinction is everything. In a vein-style deposit, a drill hole either hits the vein or misses it. In a porphyry like Maria Bonita, the mineralisation runs through virtually the entire rock mass, interrupted only by minor non-mineralised feldspar porphyry intrusions. Altamira reports that drilling roughly every 100 metres is sufficient to define the resource because the gold is so continuous.

The company characterises Maria Bonita as “Brazil’s first confirmed porphyry gold deposit,” a description that underlines how unusual the asset is within Brazilian gold exploration. Discovery-stage results included intercepts such as 146 m at 1 g/t Au from 23 m, the kind of long, continuous grade that defines this style of system.

Illustrative intercept: 146 m at 1 g/t Au from 23 m depth, a single hole demonstrating the continuous mineralisation typical of the deposit.

The key geological features driving the efficiency are worth setting out plainly:

• Porphyry-hosted, with gold distributed broadly through the rock
• Continuous mineralisation with near-total involvement of the porphyry body
• A low waste-to-mineralised material ratio of approximately 0.4:1
• The deposit remains open to the west, south, and at depth

That open geometry matters. In August 2026, drill holes MBA-040 to MBA-043 confirmed a new mineralised porphyry body at Maria Bonita West, evidence that the system extends beyond the current pit shell. The same geological continuity that makes each metre so productive also gives the deposit a plausible growth runway.

The read for you is this. If the porphyry is genuinely as continuous as drilling suggests, future campaigns should keep adding ounces efficiently until the deposit boundaries are defined. But those additions land mostly as Inferred material, which still requires conversion drilling before it can support mine planning.

The gold price factor: how US$4,150/oz changes the arithmetic for low-grade bulk-tonnage deposits

Rewind to 2019. Altamira’s original resource calculation used a gold price of US$1,500/oz, and at that price the deposit held roughly 700,000 ounces considered economically mineable. The rock has not changed dramatically since. The price of gold has.

The structural shift in gold miner profitability at prices above US$3,000/oz is precisely why the pit-shell assumption at Maria Bonita has moved from US$2,780 to US$3,300 in fourteen months, with current spot sitting meaningfully higher still and expanding the economic case for low-grade bulk-tonnage ore.

The progression tells the story:

1. 2019: US$1,500/oz assumption, roughly 700,000 oz resource
2. May 2025 maiden MRE: US$2,780/oz pit-shell assumption
3. September 2026 updated MRE: US$3,300/oz pit-shell assumption
4. Current spot: US$4,150-US$4,300/oz

For a low-grade, high-tonnage porphyry, the mechanical relationship between gold price and resource size is direct. As the assumed revenue per tonne rises, marginal blocks of rock that were previously sub-economic move inside the economic boundary. The optimised pit shell deepens and widens, and more tonnage gets classified as resource.

That mechanism explains much of the Inferred tonnage tripling from 25.64 Mt to 70.0 Mt. The US$520/oz increase in the pit-shell assumption between the maiden and updated estimates, from US$2,780 to US$3,300, pulled a large volume of lower-grade material into the economic pit.

Management view: Mike Bennett of Altamira Gold noted at the Beaver Creek Precious Metals Summit in September 2026 that a gold price of around US$3,000/oz would be sufficient to make developing the resource substantially easier.

Here is where you need to be careful. The updated pit-shell assumption of US$3,300/oz sits well below current spot, which provides a genuine buffer. But it still sits above many long-term consensus price forecasts. If gold retraces significantly, the pit shell contracts, the cut-off grade rises, and some of those newly added Inferred ounces fall back outside the economic boundary. For any low-grade resource, price sensitivity is as material to the risk picture as the headline ounce count itself.

What the growth story still needs: five risk factors investors should price in

The resource growth is real, but so is the gap between where the project stands and where it needs to go. These are the unresolved variables, not dealbreakers, that separate current geological potential from a development-ready asset.

• Inferred weighting and conversion requirement: Approximately 69% of the resource (908,477 oz of 1,312,354 oz) sits in the Inferred category, the lowest confidence level, which cannot support reserves or detailed mine planning until converted through further drilling.
• Gold price sensitivity: The pit-shell economics depend on elevated price assumptions, and a reversion toward long-term consensus prices would shrink the pit and the economic resource.
• Absence of a PEA or PFS: No preliminary economic assessment or pre-feasibility study has been published as of September 2026, so the resource has not been tested against real capital costs or metallurgical performance.
• Brazilian permitting and land access: Open-pit projects with large footprints face environmental review requirements, and land access for western targets is a current operational focus.
• Junior financing conditions: Explorers rely on equity and strategic investment, and a large Inferred resource attracts attention but does not guarantee access to capital.

The first of these is the structurally important one. Converting a large Inferred inventory to Indicated or Measured requires substantial additional drilling and cost, and conversion can downgrade grade or tonnage if geological continuity proves weaker than early models assumed.

The CIM Definition Standards for Mineral Resources establish that Inferred material carries the lowest geological confidence of the three resource categories, and cannot underpin ore reserves or the economic modelling required for a pre-feasibility study without first being upgraded through systematic infill drilling.

Permitting, financing, and the path from ounces to economic studies

Brazil’s environmental and permitting processes for large open-pit projects can be lengthy, and timelines are difficult to predict at the resource stage. Altamira has flagged land access as an active step, with work underway on western Cajueiro targets including Novo Sonho, located roughly 3 km west-southwest of Maria Bonita.

Brazil’s mining regulatory reforms in 2026 have introduced fast-track pathways for projects classified as critical mineral producers, a development that could materially affect the permitting timeline for large open-pit gold projects like Maria Bonita if the classification applies.

Financing is the other unresolved question. Rapidly growing resources can draw interest from larger producers and strategic investors, but that interest is not guaranteed. The 0.4:1 strip ratio is a genuine positive for future economics, yet without a PEA the 1.31 Moz figure has not been stress-tested against capital expenditure, infrastructure, or metallurgy. Until it is, treat the current valuation as exploration-stage pricing, an option on future value rather than a confirmed pathway to production.

What a resource that doubles in 14 months tells you about the next phase

An 82% increase in total ounces, from 720,200 oz to 1.31 Moz, achieved in roughly 14 months of incremental drilling, sets up the next phase rather than concluding the story. The question now is not whether the resource can grow further; the geology makes continued additions likely. It is whether the company can convert exploration momentum into economic clarity before conditions shift.

The gap between headline ounces and bankable value is a recurring theme across South American gold development stories; the resource investor metrics that matter most are confidence category weighting, cut-off grade sensitivity, and the distance to an economic study, not the total ounce count alone.

Three milestones will define the development arc over the next 12-18 months:

1. Indicated conversion drilling results: how efficiently current Inferred ounces move into higher-confidence categories
2. PEA publication timeline: the first real test of the resource against capital costs and margins
3. Maria Bonita West and Novo Sonho drill results: whether the system keeps extending along its open boundaries

Growth runway: The deposit remains open to the west, south, and at depth as of September 2026, with additional drill rigs planned for site to accelerate the programme.

The project sits at a geological inflection point where continued drilling may well be the right use of capital. But with no economic studies yet published, the market is pricing exploration upside, not development certainty. Knowing which milestones to watch, and in what order, gives you a basis for re-evaluating the position as new information lands, rather than reacting only to the next headline ounce count.

This article is for informational purposes only and should not be considered financial advice. Investors should conduct their own research and consult with financial professionals before making investment decisions. Past performance does not guarantee future results. Financial projections are subject to market conditions and various risk factors, and forward-looking statements are speculative and subject to change based on market developments and company performance.