This report details the mineral processing and recovery methods at an underground polymetallic mine in Alaska.
Report context
The Greens Creek Mine, located near Juneau, Alaska, USA, is the subject of this NI 43-101 Technical Report with an effective date of December 31, 2018, and filed April 1, 2019. The report documents the property description, geological setting, mineral resources and reserves, mining methods, and recovery methods for this polymetallic operation. The processing sections draw upon historical operating data, proposed design parameters, and metallurgical testwork.
Processing route
Process flow sheet
The recovery methods section of the report describes the process flow sheet and plant description for the Greens Creek operation. The processing plant includes secondary grinding and a gravity circuit as key components of the comminution and concentration stages.
Flotation circuits
The flotation circuits are a central element of the processing route. The report documents that reagents are used within the flotation circuits. The flotation process is followed by dewatering stages. The report details that product and materials handling systems are in place for the concentrate output.
Metallurgical test work
The mineral processing and metallurgical testing section (Section 13.0) documents the metallurgical test work conducted for the operation. Recovery estimates are reported, including information on historical performance. The report notes a flotation strategy advancement program and optimization work related to Net Smelter Return (NSR) estimation. Projected life-of-mine (LOM) recoveries are presented based on this work.
Metallurgical variability
The report documents mill feed variability as a consideration in processing. The presence of backfill materials in mill feed is identified as a factor. A testwork composite approach was used to evaluate metallurgical performance.
Deleterious elements
The report identifies the presence of deleterious elements and their consideration in the processing strategy.
Key reported parameters
| Parameter | Unit | Design/Proposed | Historical Actual | Testwork Basis |
|---|---|---|---|---|
| Recovery estimates (projected LOM) | , | Reported | Reported | From metallurgical test work |
| Flotation circuit configuration | , | Described | Operating data | From test work |
| Secondary grinding | , | Included in plant description | Operating data | From test work |
| Gravity circuit | , | Included in plant description | Operating data | From test work |
| Reagent usage | , | Described | Operating data | From test work |
| Dewatering | , | Described | Operating data | From test work |
| Product handling | , | Described | Operating data | From test work |
| Energy, water, and process materials requirements | , | Reported | , | , |
| Mill feed variability | , | , | Documented | From testwork composites |
| Backfill materials in mill feed | , | , | Documented | From testwork composites |
Project website: https://www.hecla.com/operations/greens-creek-alaska
Technical qualifications
The report includes a cautionary statement on forward-looking information, noting that forward-looking statements are based on opinions and estimates made as of the date such statements are made and are subject to important risk factors and uncertainties, many of which cannot be controlled or predicted. Material assumptions regarding forward-looking statements are discussed in the report. The report also contains cautionary statements regarding differences between U.S. Securities and Exchange Commission Guide 7 reporting requirements and Canadian NI 43-101 standards for mineral reserve and mineral resource disclosure. The processing and metallurgical information is derived from the original technical report sections on mineral processing and metallurgical testing, and recovery methods, with the understanding that operating data represents historical conditions and that projections are based on available testwork and optimization studies.
Source: Technical Report for the Greens Creek Mine, Juneau, Alaska, USA, NI 43-101 Report, effective date December 31, 2018, filed April 1, 2019, Sections 1.9, 13.0, and 17.0.
