Midas Gold Corp. today provided an update on the feasibility-level metallurgical testing program being carried out on its Stibnite Gold Project ("Project"), which is located in Idaho, USA. This work is an important foundation for the planned feasibility study ("FS") for the Project. The metallurgical testing program, being conducted at several laboratories in the Vancouver, B.C. area, is being coordinated by Blue Coast Metallurgy Ltd. ("Blue Coast") under the guidance of a team of metallurgical experts working with Midas Gold's technical staff.
The current metallurgical testing program is designed to achieve the following objectives:
- Enhanced economics for the Project by reducing capital and operating costs, improving the antimony concentrate grade, and improving gold flotation recoveries as compared to those reported in the December 2014 prefeasibility study ("PFS"); and
- Geo-metallurgically model the projected metallurgical response (throughput and recoveries) spatially across the different mineral deposits. A robust geo-metallurgical model would further reduce metallurgical risk to the Project and may create opportunities to enhance overall Project economics.
Metallurgical Testing Program
To date, the focus of the testing has been on optimisation of the grinding and flotation stages of the Project. This work has utilized composites comprising 237 intervals from 29 drill holes, and was designed to create composites that closely represent (by grade, lithology, and spatial distribution) the expected mix of ore through the first 3 years of the projected production as detailed in the PFS. As such, these composites are the most representative metallurgical composites of likely ore in the early years created for the Project testing programs to date.
Results to Date
Based on the flotation and grinding work completed to date, several encouraging results have been achieved:
- Reagent dosages and overall consumption of flotation reagents have been significantly reduced without negatively affecting metallurgical performance. This should translate into reduced life-of-mine operating costs as compared to the doses used in the PFS, estimated in the range of US$20-30 million based on assumptions in the PFS.
- The target primary grind has been coarsened from 75 to 85 microns without negatively affecting metallurgical performance. This should result in reductions in both capital and operating costs as compared with the primary grind size employed in the PFS.
- Antimony concentrate grades have been improved. In the case of the Yellow Pine deposit, antimony concentrate grades are projected to increase from 59% antimony by weight in the PFS to 63-65%, with similar overall antimony recoveries, while gold losses to the antimony concentrate have been reduced, increasing overall payable gold recoveries for the Project as compared to the PFS. Higher antimony concentrate grades would reduce concentrate shipping costs and enhance the marketability of the concentrate, which should lead to more favourable contractual rates from buyers.
- Overall reported gold flotation recoveries have increased. Based on tests using the enhanced processing conditions, gold flotation recoveries for the Yellow Pine and Hangar Flats deposits have been several percentage points higher as compared to the PFS. Materials from the West End deposit have not been sufficiently tested to confirm that the increased gold flotation recovery trend applies to that deposit.
"The results of the metallurgical optimization test work completed to date on our Stibnite Gold Project are encouraging," said Stephen Quin, President & CEO of Midas Gold Corp. "This test work represents one of a number of avenues for enhancing Project economics that we are pursuing. Other avenues include the mineral resource optimization drill program currently in process and optimizing development rock storage, as well as the balance of the metallurgical test program still to be completed."
Test work to optimise the grinding and flotation circuits is nearly complete, and attention is now moving to the pressure oxidation and downstream hydrometallurgical circuits. The aim of this next stage of test work is to enhance Project economics, largely through a combination of reduced projected capital and operating costs as compared to the PFS. This work, which includes piloting of both the mineral processing and autoclave stages of the Project plus considerable batch testing to support process design, is expected to be complete by mid-2017.
A detailed geo-metallurgical program is underway to model the potential variability in metallurgical performance in the process. Project geologists and metallurgists are collaborating closely to establish how the expected process response of all mineralised material within mineral resources can be modelled spatially by comparing various rock types, alteration styles and geochemical analyses with metallurgical performance. Ultimately, this modelling should support the projection of throughput and metallurgy for every block in the mineral resource and mine plan. This modelling is expected to both reduce metallurgical risk to the Project and open the opportunity for development of a mine plan that, where possible, exploits optimal metallurgical performance early in the life of the Project.
Details of the previous news releases, the Project and the 2014 Preliminary Feasibility Study can be found filed under Midas Gold's profile on SEDAR (www.sedar.com) or at www.midasgoldcorp.com.
Quality Control and Quality Assurance
The technical information in this news release has been prepared in accordance with Canadian regulatory requirements set out in National Instrument 43-101 ("NI43-101") and reviewed and approved by Stephen P. Quin, P. Geo., President and CEO of Midas Gold Corp., and a Qualified Person. The metallurgical testing program for the Stibnite Gold Project was carried out under the supervision of Christopher Martin, MIMMM, C.Eng., a Qualified Person and Principal Metallurgist for Blue Coast Metallurgy Ltd.