GR Silver Mining: The Plomosas MIA Waiver and What It Means for San Marcial

• Mexico's Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT) has confirmed that no new Environmental Impact Authorisation (MIA) is required for the Plomosas Bulk Sampling Test Mining (BSTM) program at GR Silver Mining, citing existing infrastructure, no change in land use, and no expected increase in environmental risk. Only secondary permitting, already in process, now stands between the company and pilot plant installation.
• The MIA waiver matters most for San Marcial, not Plomosas. San Marcial is an exploration concession facing a 5 to 7-year permitting pathway to production. Management has stated that a demonstrated regulatory compliance record at Plomosas is the mechanism to shorten that timeline, with each year removed potentially accelerating cash flows and increasing the project's net present value (NPV).
• The company's best-ever drill result at San Marcial returned 45.1 metres true width at 1,623 grams per tonne silver, with the system remaining open along 80% of the untested intrusive perimeter. The planned MRE update will quantify whether step-out drilling has added to the 2023 base of 134 million silver equivalent ounces.
• GR Silver Mining is fully funded with C$28.5 million in cash and no debt, with 4 catalysts sequenced through to the first half of 2027: completion of the 20,000-metre drill program, pilot plant installation, a Mineral Resource Estimate (MRE) update, and a Preliminary Economic Assessment (PEA).
• Following the passing of founder Márcio Fonseca, Eric Zaunscherb has resigned as Executive Chair to focus exclusively on his duties as Interim President and Interim Chief Executive Officer, and Larry Taddei has been appointed Lead Independent Director. Three drill rigs remain active, and all programs are continuing.

What Has Happened

GR Silver Mining (TSXV: GRSL, OTCQB: GRSL, FRA: GPE) announced that SEMARNAT has confirmed that no new Environmental Impact Authorisation (MIA) is required for the Plomosas Bulk Sampling Test Mining (BSTM) program, citing existing infrastructure, no change in land use, and no expected increase in environmental risk. The decision removes a major permitting hurdle, leaving only secondary permits, already in process, before the company can proceed with installing a pilot plant at the former Plomosas underground mine.

What the waiver means for San Marcial is the more consequential question. Plomosas is a mining concession with existing permits and 7.4 kilometres of underground development; it was always the nearer-term asset. San Marcial is an exploration concession that could require 5 to 7 years of permitting before reaching production. By confirming the Plomosas infrastructure as a sufficient basis for pilot plant operations, the waiver removes the primary barrier to establishing the regulatory track record management has stated is the mechanism to shorten that timeline. Combined with the company's best-ever drill result at San Marcial, the waiver advances both conditions required for San Marcial's development: permitting progress and resource growth.

The Permitting Logic: Why Plomosas Unlocks San Marcial

The BSTM program at Plomosas is not a production vehicle. A 60- to 100-tonne-per-day pilot plant generates limited ounces and cash. Its value is the regulatory track record it creates with SEMARNAT and state authorities - a record management has stated can shorten the 5 to 7-year permitting timeline that would otherwise apply to San Marcial as an exploration concession. Every year removed from that timeline accelerates potential cash flows, directly increasing the project's net present value (NPV)

Interim President and Interim Chief Executive Officer of GR Silver Mining, Eric Zaunscherb, explained the mechanism:

"It's not a lot, it's not going to generate a lot of ounces, it's not going to generate a lot of cash, but it does generate some cash, and so the idea is social license. There's another important feature here, and that is that while Plomosas is a mining concession, San Marcial, however, is an exploration concession. In today's environment, to permit that and get that into a producing state, going through all the technical studies and permitting process could be 5 to seven years. However, if we proceed with the bulk sample testing program at Plomosas and demonstrate to the regulators that we are doing a good job there, we're employing people there, then there's an opportunity to make that process for permitting and technical studies for San Marcial shorter, and that obviously has a big impact on the NPV of the project."

The MIA waiver confirms SEMARNAT's acceptance of the existing Plomosas infrastructure as sufficient to proceed without a new environmental authorisation, removing the primary permitting step between the company and pilot plant commissioning.

San Marcial Geological Update: Best-Ever Drill Results

The 2026 step-out program returned its standout result, with 45.1 metres true width at 1,623 grams per tonne silver, including 18.85 metres at 3,846 grams per tonne silver, and a highest-grade core of 8.25 metres at 8,579 grams per tonne silver, with 1.6% lead and 5.5% zinc. A secondary intercept of 20.6 metres true width at 32 grams per tonne silver confirmed mineralisation persists below 328 metres depth. Earlier 2026 step-out results demonstrated grade continuity to a depth of approximately 500 metres along the southeast extension, with multiple intervals returning silver grades above 350 grams per tonne.

The 2023 NI 43-101 Mineral Resource Estimate (MRE) established a combined base of 134 million silver equivalent ounces across the Plomosas Mine Area and San Marcial Area. Management has stated that only approximately 20% of the perimeter around the central intrusive body has been drilled to date, leaving 80% untested. The current 20,000-metre program is approximately 5,000 metres complete, with 3 rigs active and road upgrades from Durango targeting the addition of further rigs. The planned MRE update will quantify whether the 2026 step-out drilling has added to the 134 million silver equivalent ounces established in 2023.

Operational & Jurisdictional Risk Factors

Secondary permitting for the BSTM program is in process, and its timeline has not been publicly disclosed. Pilot plant acquisition and installation remain subject to both the completion of secondary permits and prevailing security conditions. Access constraints in Sinaloa are a stated factor in the final timing of the drill program, MRE update, and PEA, with the company noting final timing is "dependent upon ongoing access".

To reduce personnel exposure in Sinaloa, the company established Durango City as its logistical base, with the principal secondary road from Durango to the project currently being upgraded to support faster supply and egress. 

Zaunscherb quantified the security adjustment:

"The pivot that Márcio began in November of last year, the pivot to working out of Durango, has been extremely important in reducing our risk profile. One comes through Durango, and it's only the last few kilometres that are in the state of Sinaloa."

Execution & Capital Position

Three drill rigs remain active, the BSTM engineering studies are complete, and secondary permitting is in process. All programs are continuing under interim leadership following the passing of founder Márcio Fonseca. Zaunscherb has formally resigned his Executive Chair position to focus exclusively on his Interim President and Interim Chief Executive Officer duties, a governance step the company described as best practice. Director Larry Taddei, a Chartered Professional Accountant and former Chief Financial Officer of MAG Silver Corp. from 2010 to 2022, has been appointed Lead Independent Director.

Zaunscherb addressed the continuity of the on-ground team:

"I think for them the continuity is important. They are there, they're extremely talented, they've got the experience with the property, and they're enthused. They're so excited about the project, they want to continue to work on it, so I think they feared with Márcio passing that there'd be a big pause as we dropped back and punted. That's not going to happen."

As of May 29, 2026, GR Silver Mining holds C$28.5 million in cash with no debt. At C$0.40 per share, the undiluted market capitalisation is C$204 million. The same presentation notes that the company is trading at US$1.65 per silver-equivalent ounce, compared with a peer mean of US$3.43 per silver-equivalent ounce.

What to Watch Next

Near-term catalysts include additional step-out drill results as 3 rigs remain active on the 20,000-metre San Marcial program - approximately 5,000 metres complete as of the June 2026 interview - and a pilot plant purchase announcement, which would confirm the BSTM timeline and the commencement date for building the regulatory record at Plomosas. The company is targeting completion of the drill program in the second half of 2026, to be followed by an MRE update that quantifies the resource position relative to the 134 million silver-equivalent ounces established in 2023. The PEA, targeting the first half of 2027, will integrate the Plomosas Mine Area and San Marcial Area into a combined development scenario and produce the first published NPV for the project - the first formal basis on which the value of any San Marcial permitting acceleration can be measured.

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