01:00 PM EDT, 05/15/2018 (MT Newswires) -- Osisko Mining (OSK.TO) was down 20% to the lowest since late 2016 Tuesday after the company late Monday released a resource estimate for its Windfall gold deposit in Quebec showing the site contains indicated resources of 601,000 ounces.

The estimate is Osisko's first for the project and comes from the results of 596,733 meters of exploration drilling from more than 1,400 holes using a grade cutoff of 3 ounces of gold per tonne.

The estimate, which separately pegs a less-definite indicated resource 2.28 million ounces, disappointed investors who had expected a more substantial figure following months of the company releasing drill results for the property showing gold values of up to 611 grams per tonne of gold over short stretches of core.

Osisko said it will release a preliminary economic assessment for Windfall and the neighboring Osborne-Bell deposit early in the third quarter.

Osisko Mining was last seen down $0.55 to $2.15. The shares have now dropped 56% over the past 12 months.

Price: 2.18, Change: -0.52, Percent Change: -19.26