Mineral processing for the Fire Creek Project relies on third-party milling at the Midas Mine, with metallurgical testwork completed between 2011 and 2017.
Report context
This technical report, dated September 14, 2018, with an effective date of March 31, 2018, was prepared for Hecla Mining Company following its acquisition of Klondex Mines Ltd., announced on March 19, 2018. The report presents an updated Mineral Resource and Mineral Reserve estimate for the Fire Creek Project, located primarily in Lander County, Nevada, approximately 63 miles west of Elko. The report includes processing information based on testwork and existing mill facilities.
Processing route
Mill Capacity and Process Facility Flow Diagram
The Fire Creek mineralized material is processed at the Midas Mill, a conventional Merrill Crowe mill facility capable of processing 1,200 tons per day. A process facility flow sheet diagram was prepared by Klondex in 2015.
Physical Mill Equipment
Process equipment is itemized by area within the mill facility. The Midas Mill is described as an efficient, well-maintained modern mineral processing plant that operates with a minimum crew.
Operation and Recoveries
Metallurgical recoveries applied to Mineral Reserves are 93% for gold and 88% for silver. Underground Mineral Resources were calculated using metallurgical recoveries of 94% for gold and 92% for silver. Open pit Mineral Resources used recoveries of 65% for gold and 30% for silver for oxide mineralization, and 60% for gold and 25% for silver for mixed mineralization.
Tailings Storage Capacity
The report references tailings storage capacity as part of the Midas Mill infrastructure.
Processing Costs
Midas Mill operating costs are reported in a dedicated table within the report.
Production
Historical Fire Creek mineralized material processed at the Midas Mill is tabulated in the report.
Midas Mill Operating Permits
The Midas Mill operates under its own set of permits, which are referenced in the report.
Early Test Work
Cyanidation test results from the 2011 technical report are summarized. Combined metallurgical results from gravity and cyanidation tests, with feed ground to 80% passing 212 micrometers for gravity concentration and reground to 80% passing 75 micrometers for cyanidation, are reported.
2013 Test Work
Bottle roll tests were conducted on Fire Creek West Zone drill core composites. A summary of metallurgical results from these tests is provided in the report.
2014 Test Work
Whole mineralized material was tested using gravity concentration with cyanidation of the gravity cleaner and rougher tailings. Gold and silver metallurgical results from this testwork are tabulated separately in the report.
2017 Test Work
Bottle roll tests were conducted on Fire Creek Mars Pit drill core composites for oxide, mixed oxide/sulfide, and sulfide material types. Summary metallurgical results for each material type are reported in dedicated tables.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Mill capacity | 1,200 tons per day | Design |
| Gold recovery – Mineral Reserves | 93% | Design |
| Silver recovery – Mineral Reserves | 88% | Design |
| Gold recovery – Underground Mineral Resources | 94% | Design |
| Silver recovery – Underground Mineral Resources | 92% | Design |
| Gold recovery – Open pit oxide | 65% | Design |
| Silver recovery – Open pit oxide | 30% | Design |
| Gold recovery – Open pit mixed | 60% | Design |
| Silver recovery – Open pit mixed | 25% | Design |
| Gravity/cyanidation test feed size | 80% passing 212 micrometers | Testwork |
| Regrind size for cyanidation | 80% passing 75 micrometers | Testwork |
Project website: https://www.hecla.com/exploration/nevada-usa
Technical qualifications
The report notes that the Midas Mill is an efficient, well-maintained modern mineral processing plant capable of processing 1,200 tons per day, with underutilized processing capacity that can accept increased mine production. The mill operates with a minimum crew, which results in cost reductions when operated at capacity.
The process facility flow sheet diagram was prepared by Klondex in 2015 and is included in the report as Figure 17-1.
Source: Technical Report for the Fire Creek Project, Lander County, Nevada, dated September 14, 2018, Sections 13, 17, and related tables.
