The channel sample was made adjacent to an existing room and pillar stope into unmined zones and returned 5.4m grading 1,313 grams per tonns silver-equivalent, including 1m grading 4,204g/t.
"These new high-grade polymetallic underground channel sampling results are extraordinary, indicating the potential to define substantial new mineralised zones," said president and CEO Marcio Fonseca.
"The geological setting of these samples provides an opportunity to define large volumes of not only precious metals, but also base metals.
"The presence of gold that appears to be associated with base metal mineralisation, provides immediate new underground and surface drilling targets, aiming to delineate much larger resources in the near future."
The company plans to undertake more underground channel sampling, geological and structural mapping, and underground drilling. An initial 1,400m underground core drilling programme is expected to continue through 2020 and focus on the delineation of new areas for resource estimation.
Shares in GR Silver Mining are trading at C65c, valuing the company at $80 million.