Since the discovery of Ixtaca in 2010, Almaden has initiated several metallurgical test programs. As reported in a news release updating our pre-feasibility test work on October 31st, 2016 work to date confirms a likely flow sheet of gravity and flotation to produce a concentrate for either off site refining or subsequent leaching to create a gold-silver doré.
The Ixtaca deposit gold and silver mineralisation occurs as electrum (a gold/silver alloy) and gold and silver bearing sulphides in epithermal veins and veinlets cutting carbonate (limestone and shale) and volcanic rocks.
By way of background, in our Pre-Feasibility Study ("PFS") announced on April 3rd, 2017, limestone comprises 82% of the metal produced, volcanic 8% and blackshale 10% on a gold-equivalent basis using a 69:1 silver to gold ratio.
Mill feed during the initial capital payback period of the PFS mine plan is made up of limestone and volcanic-hosted mineralization. There is negligible disseminated mineralisation in the carbonate rocks which host the majority of the gold and silver vein mineralisation, the remainder of which occurs in the overlying altered volcanic units.
Gold and silver mineralogy vary little within domains and grade varies according to the density of veining. The detailed mineralogy and geologic observations carried out before metallurgical test work indicated the opportunity to pre-concentrate electrum and precious metal bearing sulphides to create a gold silver concentrate.
The focus of the ongoing metallurgical test work program has been on the limestone material, which has been tested across a range of gold and silver grades. As mentioned above, limestone represents 82% of the metal produced in the PFS Base Case pit, and the bulk of the payback material.
Recent results are consistent with past results and confirm 90% recoveries for gold and silver in the limestone material, with declining reagent consumption as optimization advances.
Testing announced on October 31 2016 was conducted on a limestone sample using 131 meters (659 kilograms) of continuous whole drill core from inside the planned open pit mine with an average sample grade of 0.76 g/t gold and 36 g/t silver. The sample was collected from the planned start-up pit area and represents limestone mill feed grades anticipated in the first 5 years of mining. Results demonstrated:
Ongoing limestone metallurgical test work will focus on demonstrating the repeatability of the above gravity and flotation results, and continuation of the leach circuit optimization program. Test work will then expand to the smaller metallurgical domains (Volcanics and Black Shale).
The work is being carried out at McClelland Laboratories in Reno Nevada under the supervision of independent engineers Moose Mountain Technical Services (“MMTS”) and qualified person Tracey Meintjes, P.Eng. of MMTS.