A 300-Meter Extension at San Marcial Sets Up GR Silver's 2027 Resource Update

• Step-out drilling in the southeast area returned 16.1 meters (m) true width at 162 grams per metric ton (g/t) silver and 11.7 m true width at 147 g/t silver.
• The results extend the mineralized breccias at least 300 m to the southeast and 75 m down-dip beyond the 2023 resource boundary.
• The breccia system is now known to extend about 1 kilometer along its strike length.
• High-grade zones occur where northeast-southwest structural trends intersect northwest-southeast and east-west hydrothermal breccias.
• The 2026 program has drilled 6,292 m in 21 holes, with assays pending from 7.
• GR Silver is targeting a mineral resource estimate update in the first half of 2027.

Company Overview

GR Silver Mining (TSXV: GRSL | OTCQX: GRSLF | FSE: GPE) is a Canadian-based, Mexico-focused mineral exploration company working on silver-gold resource expansion at its 100%-owned assets on the eastern edge of the Rosario Mining District, in the southeast of Sinaloa State, Mexico. The company controls 100% of the Plomosas Project, which includes the high-grade silver discovery at the San Marcial Area and the former Plomosas underground mine, together with 78 square kilometers of advanced-stage exploration concessions.

High-Grade Silver Beyond the 2023 Resource Boundary

Step-out drilling in the southeast area at San Marcial returned 16.1 meters (m) true width at 162 grams per metric ton (g/t) silver from 375.05 m downhole, including 0.7 m at 1,344 g/t silver. A second hole returned 11.7 m true width at 147 g/t silver from 275.55 m downhole, including 2.85 m at 429 g/t silver.

Both intercepts lie outside the boundary of the 2023 mineral resource estimate (MRE). Together they extend the mineralized breccias at least 300 m to the southeast and 75 m down-dip from that boundary, taking the known strike length of the breccia system to approximately 1 kilometer (km). The mineral assemblage indicates that mineralization may continue beyond the currently defined limits.

The mineralization is hosted in chlorite-hematite hydrothermal breccias at the contact between the upper Oligocene volcanic sequence and the lower Jurassic volcano-sedimentary unit. Stockwork veinlets within the Jurassic unit show that high-grade silver is not confined to the contact zone itself. The vertical extension of the system is also supported by earlier holes on the same section, which returned 112.6 m at 61 g/t silver and 11.3 m at 584 g/t silver.

How the High-Grade Zones Are Controlled

Four further holes established that the high-grade zones are strongly structurally controlled. They occur where northeast-southwest structural trends intersect northwest-southeast and east-west hydrothermal breccias, and silver grades fall away outside those intersections.

That finding is being applied to the 20,000 m step-out program to guide where the next holes go. Andesitic and dioritic dikes carrying silver mineralization become more common toward the southeastern end of the area, and the silver and lead-zinc mineralization crosscuts both dike types, which places the mineralizing fluids after the Oligocene intrusive complex was emplaced.

The dikes support a model in which the breccias relate to an underlying intrusive body, with a possible transition from an epithermal system to a porphyry-style system at depth. Geochemical and structural vectoring studies are underway to evaluate that potential beneath the San Marcial breccia.

A System That Plunges Southeast 

A hole about 80 m above the second of the two intercepts cut a broad zone of lower-grade material, 36.0 m at 15 g/t silver. The system approaches surface with lower grades and widens and strengthens at depth, which confirms an inclined plunge toward the southeast.

Alteration intensity, mineral assemblage and structural indicators in those two holes point to mineralization that remains open at depth, with no indication that grade or intensity falls off. Subsequent holes in the program will test that interpretation.

Drill Program Progress

The 2026 step-out program has drilled 6,292 m in 21 holes at San Marcial, with assays pending from 7 of them.

President and Chief Executive Officer of GR Silver Mining, Eric Zaunscherb, ties the drilling to what the company plans to publish next: 

"We continue to be very pleased with the results of our 20,000-m step-out drill program at San Marcial and the efficacy of our geological model. This mineralized system is proving to be very extensive, and we are confident in seeing a significant result in our planned MRE update in the first half of 2027."

Zaunscherb also accounts for the rate at which the meters have been drilled:

"The pace of the drill program has been affected by the additional distance to access the Project from our new base in Durango, intermittent security issues in Sinaloa and surrounding areas, and exacerbated by the ongoing wet season. We have launched several initiatives to re-accelerate the pace, which should bear fruit in the fourth quarter."

A slower pace also lets the company respond to assays as they arrive and reposition later holes.

Next Steps 

The next holes will continue to test the continuity of high-grade silver at depth. Future drilling will also test in the vicinity of an earlier intercept of 45.1 m true width at 1,623 g/t silver, including 8.25 m at 8,579 g/t silver, along with several other nearby structural targets.

GR Silver is targeting an MRE update in the first half of 2027.

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