The report was prepared by CSA Global under contract to SLR Consulting Ireland and was based on 88 diamond holes carried out by Teck Resources, which was the previous operator from 2007 to 2011.
The estimate is 5.3mln tonnes at a grade of 11.15% zinc and lead combined (8.55% zinc and 2.60% lead) in the lower confidence inferred category.
The bulk of the tonnage lies in the high-grade StonePark North orebody which contains 4mln tonnes grading 11.95% zinc and lead (9.10% zinc and 2.86% lead) and lies 190m to 240m below surface.
"This maiden mineral resource marks a significant milestone for Group Eleven as it demonstrates not only very attractive grades in a global context, but also significant tonnage from an Irish perspective.
"Past producing Irish zinc mines, Tynagh and Galmoy, for example, were about 10mln tonnes in size" said Bart Jaworski, chief executive.
"At Stonepark, the relatively continuous and shallow nature of the mineral resource is particularly interesting given its immediate proximity to Glencore's Pallas Green deposit - one of the largest undeveloped zinc deposits in the world.
Jaworski continued: "Pallas Green is substantially deeper than Stonepark.
"With the Stonepark resource still open along and across strike, five compelling regional targets within a 10km-radius of the Stonepark resource and several other targets on our adjacent PG West property, we view the maiden mineral resource at Stonepark as only an initial stepping stone towards unlocking the full potential of the Limerick Basin.
"The upcoming Tellus airborne survey over the Limerick and Silvermines region will be especially critical in helping to narrow down prospective structural corridors and greatly advance our regional 'Big Think' initiative."
The Stonepark mineral resource estimate is contained within three main zones - Stonepark North, Stonepark West and Stonepark.
Group Eleven also updated on drilling, with the ongoing initial phase progressing well.
At Stonepark, drilling began last week, and the firm intends to release results from Ballinalack and Stonepark over the next few weeks upon completion of logging, sampling and assaying of the core.
Also, on Tuesday, the firm announced the appointment of Dr Mark Holdstock as project manager, reporting to chief operating officer David Furlong.
Shares eased 9% to C$0.15.