Osisko Mining announced the results of 135 oxygenated bottle-roll gold leaching tests and 16 crushing/grinding tests on core samples representing the mineralized zones of the Marban and Norlartic deposits, located on Marban property near the town of Malartic, Quebec.

The Marban and Norlartic deposits have combined in-pit resources estimated at 37.0 Mt at 1.24 g/t Au for 1.48 Moz in the measured and indicated categories and 3.6 Mt at 1.15 g/t Au for 134,000 oz in the inferred category.  These resources are estimated from two optimized Whittle  pit shells at a cut-off grade of 0.40 g/t Au and using a gold price of $US 1,250 per ounce (see Osisko June 13, 2016 press release).

HIGHLIGHTS

  • Average gold recovery of 91.1% for the Marban deposit (increase of 2.8% from previous results – see NioGold July 6, 2015 press release).

  • Average gold recovery of 93.2% for the Norlartic deposit.

  • The Bond ball mill grindability tests (work index) gave an average of 11.6 kWh/t for the Marban deposit and of 12.6 kWh/t for the Norlartic deposit.

Bottle Roll Leaching Tests

A total of 135 samples (100 from the Marban deposit and 35 from Norlartic) were ground to an average grain size of 65 microns, oxygenated (pre-aerated) for one hour and leached for 36 hours.

For the Marban deposit, the results indicate an average recovery of 91.1% over a grade range of 0.24 to 4.37 g/t Au (average grade of 1.42 g/t Au) with average cyanide consumption (NaCN) of 0.07 kg/t.  The samples were separated in five populations and the results are summarized in Table 1.  Recoveries were improved due to pre-aeration of samples with respect to testing done in 2015. For the Norlartic deposit, the samples were separated in four populations and gave an average recovery of 93.2% on a grade interval of 0.39 to 3.11 g/t Au with an average grade of 1.49 g/t Au. The average cyanide consumption (NaCN) is 0.05 kg/t.

Six samples from the Marban deposit gave recovery results below 80% which are likely due to the presence of coarse gold grains. These samples are found in four of the five populations. Nevertheless, as previously established (see NioGold July 6, 2015 press release), the grade/recovery curve is near horizontal, signifying that the recovery does not decrease with lower grades. The Norlartic deposit samples show a much more homogeneous recovery and, similarly to Marban, show a flat grade/recovery curve. These gold cyanide leach test results are comparable to those obtained at the Canadian Malartic mine, located about 15 kilometers from the Marban project, for similar operating conditions utilized until 2015.

Comminution Tests

A total of 16 samples (10 from the Marban deposit and 6 from the Norlartic deposit) composed of PQ caliber core (diameter of 85 mm) were submitted for JK drop-weight tests, Bond low-energy impact tests, and Bond rod mill/Bond ball mill grindability tests.

  • The results at different grind sizes are categorized as medium to very hard for the coarse sized fraction (CWI), moderately soft to moderately hard for the medium sized fraction (RWI) and soft to medium for the fine sized fraction (BWI). The Bond Ball mill grindability tests (work index) gave an average of 11.6 kWh/t for the Marban deposit and of 12.6 kWh/t for the Norlartic deposit.

The results of the grindability tests demonstrate that the rock quality would not be problematic for a SABC circuit type commonly used in open pit operations such as the Canadian Malartic Mine.