All Samples Met or Exceeded Strength Criteria for Primary Mining Method
VANCOUVER, BC / ACCESS Newswire / July 6, 2026 / Grande Portage Resources Ltd. (TSXV:GPG)(OTCQX:GPTRF)(FSE:GPB) ("Grande Portage" or the "Company") is pleased to provide a project update for the New Amalga Gold property near Juneau, Alaska.
The company has received laboratory results for preliminary backfill strength testing of CRF (cemented rockfill) samples which were cast using material sourced from core samples drilled during previous field seasons. The waste rock lithologies in these samples were selected to be aligned with those that will be encountered during mine development as well as those which would be present in ore sorter reject material.
These samples were cast into test cylinders using a 4% cement binder content (see pictures below) and were tested for uniaxial compressive strength (UCS) after 10-day and 17-day cure times.
All samples met or exceeded the preliminary strength criteria selected for overhand longhole stoping, the primary mining method planned for New Amalga. Based on these results, the company intends to advance both the waste rock from mine development as well as the ore sorter reject rock as feedstocks for making CRF backfill.
Future testwork with greater cement proportions will be undertaken to evaluate backfill for underhand stoping, a secondary mining method which is planned to be utilized for a small proportion of New Amalga production and which requires higher-strength backfill.
Ian Klassen, President and CEO comments: "This is an important de-risking milestone. We are very pleased with results of this initial testwork, demonstrating that development waste rock and ore sorter reject rock are appropriate feedstocks to advance for structural backfill use at New Amalga. This further validates our small-footprint strategy which results in all waste and reject rock being placed back underground, avoiding the need for permanent disposal facilities on surface. This approach can be expected to not only reduce surface disturbance but also lower future reclamation obligations and simplify environmental permitting."
Additionally, geochemical testwork is currently in-progress on New Amalga core samples representing all major rock types present at the deposit to determine whether any have the potential to be reactive (acid-generating or metals leaching) over the long term. Previous limited testwork conducted in 2020-2021 on a small number of New Amalga wallrock samples showed favorable preliminary results, demonstrating significant net-acid-neutralizing potential ratios. For more details, see the company's April 28, 2026 news release "Grande Portage Resources Initiates Full Scale Geochemical Characterization Program and Backfill Testwork for the New Amalga Gold Project".