Drilling progress and tighter spacing
Led by Interim President and CEO Eric Zaunscherb, GR Silver is working to expand the resource base at San Marcial. Its drilling has included hole SMS26-04, which yielded a 45.1-meter true-width interval grading 1,623 grams of silver per metric ton, including 8.25 meters at 8,579 grams per metric ton.
Zaunscherb said the company is returning a rig to the platform used for that hole to reduce drill spacing from about 100 meters to 45 meters. The closer spacing is intended to support classification of indicated and inferred resources in that area in the upcoming estimate.
The program has progressed more slowly than planned. As of September 8, 2026, the company had completed 21 holes and was awaiting assays from seven. Management cited the longer journey from its new Durango base, intermittent security problems in Sinaloa and surrounding areas, and the wet season as reasons for the delays.
Management said it had begun initiatives to accelerate drilling in the fourth quarter of 2026. According to its statements reported by Crux Investor in October, GR Silver aims to publish results in batches approximately every five to six weeks as it completes the program.
Resource base and step-out results
The drilling program and planned resource update are intended to expand the Plomosas Project's 2023 NI 43-101 resource estimate. That estimate lists indicated resources of 55 million ounces of silver, or 85 million silver-equivalent ounces, and inferred resources of 22 million ounces of silver, or 49 million silver-equivalent ounces.
San Marcial accounts for 46 million ounces of indicated silver resources and 14 million ounces of inferred silver resources. The remaining resources are in the Plomosas Mine Area.
Other step-out results in GR Silver's September 2026 corporate presentation include hole SMS26-01, which intersected 6.45 meters grading 498 grams of silver per metric ton, starting 235.45 meters downhole. That interval included 1.2 meters at 1,618 grams per metric ton. Hole SMS26-03 returned 15.6 meters at 351 grams per metric ton from a downhole depth of 222.85 meters, including 2.5 meters at 1,395 grams per metric ton.
At the SE Extension target, hole SMS26-07 returned a true width of 21.9 meters grading 168 grams of silver per metric ton, including 6.15 meters at 447 grams per metric ton. Reporting the result on July 10, 2026, the company said it confirmed that silver mineralization extends at least 150 meters beyond the southeastern boundary of San Marcial's 2023 resource estimate.
Five-year exploration authorization
San Marcial's current drilling campaign falls under a five-year Informe Preventivo that SEMARNAT issued on September 9, 2025. According to GR Silver's management discussion and analysis for the six months ended June 30, 2026, the permit allows step-out and exploration drilling from 46 new sites within and around the existing resource area, without a limit on total meters drilled.
Elsewhere in Mexico, federal initiatives to speed project approvals accompany exploration programs by Guanajuato Silver, Torex Gold, Defiance Silver and Pacifica Silver.
Plomosas bulk sampling remains conditional
GR Silver also holds active operating permits for the former Plomosas Mine. SEMARNAT has confirmed that its operations do not require a new Environmental Impact Authorization, though additional approvals are still needed before any production can begin.
The company is planning a Bulk Sample Test Mining program with access to 21 underground sampling areas. Management is considering either buying an on-site pilot plant or using toll milling.
Plomosas was operated from 1986 to 2000 by IMMSA, a Grupo Mexico subsidiary. During that period, its crushing, milling and flotation circuit, with a capacity of 600 metric tons per day, processed 2.5 million metric tons of ore. Production totaled 67,600 metric tons of lead concentrate and 31,400 metric tons of zinc concentrate, with silver and gold credits.
Historical mining used the room-and-pillar method and reached a depth of only 260 meters. Some 7.4 kilometers of underground tunnels and development remain in good condition, offering access for exploration and potential future mining.
Before production, GR Silver must secure secondary permits, including authorization to reactivate the existing tailings storage facility. The bulk sample program also depends on studies showing it would be cash-flow positive.
