GR Silver Mining Reports Highest-Grade San Marcial Drill Results: 45.1 m at 1,623 g/t Silver

• Highest-grade drill results at San Marcial return 45.1 metres true width at 1,623 grams per tonne silver, including 8.25 metres at 8,579 grams per tonne silver, validating the geological model for high-grade silver mineralisation.
• High-grade silver mineralisation is controlled by structural intersections where E-W, N-S, and NE-SW structural trends create dilatational jogs and ore shoots within chlorite-hematite-rich hydrothermal breccias.
• Results confirm continuity of near-surface mineralisation and demonstrate that structural controls create favourable conditions for fluid migration and mineral deposition at San Marcial.
• Drilling intersected high-grade silver mineralisation within a boiling zone developed between 700 and 300 metres above sea level, plunging toward the southeast.
• Results define a high-grade structural corridor, establishing a priority exploration target for resource expansion between the Central Area and southeast extension.

Company Overview

GR Silver Mining (TSXV: GRSL | OTCQX: GRSLF | FRA: GPE) is a Canadian-based, Mexico-focused mineral exploration company engaged in cost-effective silver-gold resource expansion on its 100%-owned assets, located on the eastern edge of the Rosario Mining District, in the southeast of Sinaloa State, Mexico. GR Silver Mining controls 100% of the Plomosas Project, including the former Plomosas underground mine and wide, high-grade silver mineralised zones at the San Marcial Area. Recent discoveries in the 78 square kilometres of highly prospective, advanced-stage exploration concessions position the Company well for resource expansion at the Plomosas Project.

San Marcial Structural Controls Validated by Exceptional Silver Grades

GR Silver Mining reported drill results from the southeast area of the San Marcial deposit at the Plomosas Project in Mexico on May 19, 2026. The drilling intersected two well-defined mineralised zones located at the upper and lower contacts of chlorite-hematite-rich breccias, associated with stockwork zones and andesitic to dioritic dykes emplaced along multiple structural intersections.

The upper zone returned 45.1 metres true width at 1,623 grams per tonne silver from 267.85 metres downhole, including 18.85 metres true width at 3,846 grams per tonne silver with 0.7% lead and 2.5% zinc, and including 8.25 metres true width at 8,579 grams per tonne silver with 1.6% lead and 5.5% zinc. The lower zone returned 20.6 metres true width at 32 grams per tonne silver from 328.60 metres downhole, including 7.1 metres at 51 grams per tonne silver and 0.15 grams per tonne gold.

The exceptional silver grades highlight the strong structural control of the mineralising system and further support the exploration potential of key inflexion zones, including structural jogs and shear zones, as priority targets for additional high-grade mineralisation.

Executive Chair, Interim President and Interim Chief Executive Officer of GR Silver Mining, Eric Zaunscherb, stated:

"The exceptional results from SMS26-04 represent a major milestone in the recent exploration of San Marcial. As noted, these are the best drill results reported to date on the project and further confirm the significant high-grade silver potential of the San Marcial system. With these outstanding intersections, we are confident of significantly expanding the silver resource potential at San Marcial."

Structural Model Confirms Boiling Zone and Mineralisation Controls

The drilling confirms the continuity of high-grade silver mineralisation within the chlorite–hematite hydrothermal breccias and supports the interpretation of a boiling zone developed between 700 and 300 metres elevation above sea level, plunging toward the southeast. Based on this model, planned drill holes targeting the southeast extension are expected to intersect the boiling zone at depths ranging from approximately 600 to 200 metres above sea level. In the drilling, the calcite boiling level is characterised by overprinting mineralisation consisting of acanthite, argentite, and abundant native silver, together with galena and brown sphalerite, indicating low to intermediate-temperature precipitation conditions.

Structural comparison demonstrates that structural controls play a significant role in the distribution of high-grade silver mineralisation. Sub-horizontal flexures within the breccia create zones of reduced permeability for epithermal fluids, whereas subvertical sections enhance fluid migration and mineral deposition. These sigmoidal structural geometries generate high-grade ore shoots at the intersection of E-W, N-S, and NE-SW structural trends. The drilling was specifically designed to test one of these structural inflexion zones and has successfully validated the dilatational jog and structural intersection model.

High-grade silver mineralisation is concentrated in structural flexure zones where the strike of the breccia changes from northwest to E-W, suggesting that these zones acted as favourable pathways for hydrothermal fluid flow and mineral deposition. This structural model has been developed through systematic exploration work by the GR Silver Mining geological team, supported by external structural consultants Paula Montoya and Johannes Horner.

Near-Surface Continuity Established with Historical Drill Results

The drilling results confirm the continuity of near-surface mineralisation previously intersected, which returned 123.1 metres at 112 grams per tonne silver and 82.7 metres at 121 grams per tonne silver in historical holes. Near-surface drilling supports the structural model and represents an open shear zone with stockwork in between main breccia zones with continuous silver mineralisation and local high-grade zones.

The outstanding drilling results highlight the exploration potential between the Central Area and southeast extension and confirm the potential for resource growth. The plunge orientation connects recent drilling with other strong historical results in the area, including 75.2 metres at 260 grams per tonne silver and 101.6 metres at 308 grams per tonne silver, defining a high-grade structural corridor and a high-priority exploration target.

Next Steps

GR Silver Mining will continue step-out drilling at San Marcial in 2026, with planned drill holes targeting the southeast extension expected to intersect the boiling zone at depths ranging from approximately 600 to 200 metres above sea level. The company identified the high-grade structural corridor as a priority exploration target for resource expansion between the Central Area and southeast extension. Continuous resource growth remains the principal objective of the 2026 drilling programme at the Plomosas Project.

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