Fortuna Silver Mines Inc. presented an update of preliminary results of the optimization work being conducted on the feasibility study prepared in 2016 on the company’s 100% owned Lindero gold Project located in the Province of Salta.
Jorge Ganoza, President, CEO and Director, commented, «We are extremely pleased with gold recovery results to date as they are supportive of our initial view that the Lindero project presents significant opportunities to reduce recovery time and improve gold extraction.» Mr. Ganoza continued, «The long lead item in this optimization plan is the metallurgical process. With metallurgical tests almost completed, our engineering team is now in a position to initiate basic engineering activities on several fronts. We plan to have the project ready for a construction decision in the third quarter of 2017.»
Mineral processing optimization highlights:
- Preliminary tall-column leach tests consistently above 76% gold extraction for the four metallurgical types of ore
- Cyanide cure during agglomeration allows over 70% gold extraction in the first 30 days of leaching for the four metallurgical types of ore
- Copper concentration in solution amenable to treatment with sulfidization, acidification, recycling and thickening («SART») plant technology
- Agglomeration with modest cement addition to achieve heap heights of approximately 80 meters for 9 millimeter high pressure grinding rolls («HPGR») crushed ore
In September 2016, Fortuna started a pre-construction review of the project with the objective of optimizing certain components of the Feasibility Study. This review includes the validation of the geological model and resource/reserve estimates, optimization of the mine design, review of the metallurgical process including key metallurgy laboratory tests, and an update of the infrastructure basic engineering.
Metallurgy
Based on existing project information and preliminary results of ongoing metallurgical tests, Fortuna believes that significant improvements can be achieved in gold recovery and leach time compared to the Feasibility Study’s average gold extraction of 68% over 240 days.
Optimization of the process design has confirmed the benefit of the use of a HPGR crusher, the inclusion of cyanide cure of ore, and copper removal/ cyanide recovery with a SART plant. Results to date indicate that these components could allow for improved gold leaching kinetics and effective extraction of copper from the pregnant solution.
The table below compares preliminary gold extraction figures obtained by Fortuna as of March 20, 2017 with the Feasibility Study results. These results, estimated from solution assays, are for 10-meter tall column leaching tests that have been running for 72 days.
| Met Type | Preliminary Gold Extraction | Feasibility Study Gold Extraction
|
| 1 | 80.9% | 68% |
| 2 | 76.9% | 74% |
| 3 | 77.3% | 69% |
| 4 | 76.2% | 62%
|
() Results are based on solution assay only and are therefore preliminary in nature and final results need to be adjusted when tails assays are completed at the end of the test. Also a deduction of approximately 4% needs to be accounted for in gold extraction figures for design purposes when going from a laboratory test to commercial operation.
Final results are expected in April when assaying of tails material from the columns is completed.
Metallurgical Tests
In August 2016, samples were collected from existing drill core at Lindero and sent to Base Metals Laboratory (BML), located in Kamloops, British Columbia (Canada), for preparation which included crushing with a HPGR mill at the University of British Columbia. All preparation and tests are being carried out individually for the four metallurgical types identified in the resource as shown in the following table:
| Met Type | Met Type
Description |
Met Type Percentage
in Resource Estimation
|
| 1 | Fresh intrusive | 67% |
| 2 | Oxide porphyry | 10% |
| 3 | Fresh porphyry | 4% |
| 4 | Sediments | 19% |
A portion of the prepared material was sent to the laboratory of HydroGeoSense in Tucson, Arizona, for hydrodynamic column testwork with the purpose of evaluating permeability characteristics to determine maximum heap heights. As a result of the low to medium values obtained, agglomeration with cement is recommended to reach heap heights of approximately 80 meters. Testwork also confirmed that cement addition was sufficient for pH control during leaching, therefore no lime is required. Maximum cement consumption per metallurgical type is shown in the table below
| Met Type | Maximum
Consumption (kg/t)
|
| 1 | 4.5
|
| 2 | 4.5 |
| 3 | 1.5 |
| 4 | 0.0 |
Once optimum conditions for agglomeration were determined, leaching column testwork was initiated. The first step was a set of 32 scoping short column tests to determine the optimum leaching conditions (cyanide strength, irrigation rate, etc.) to run the 10-meter tall columns.
The company has collected core samples from a diamond drill program carried out in the third quarter of 2016 for confirmatory fresh ore column leach tests. These samples have been delivered to BML for the respective metallurgy testwork.
Mineral Reserves and Resources
The Feasibility Study was prepared as at October 23, 2015 in accordance with NI 43-101, and defines a Mineral Reserve totaling 82.5 million tonnes averaging 0.63 g/t Au and containing 1.7 million ounces of gold with a projected life of 12 years.
Fortuna has conducted a validation program which included relogging of all available drill core, heterogeneity testwork to establish the variability of the mineralization and subsequent sampling protocols, drilling of 4,461 meters to increase confidence in the geological interpretation, a geotechnical review of pit slope angle design parameters, and a re-estimation of reserves and resources. The work completed has not identified any significant changes with respect to the reserves and resources stated in the Feasibility Study.
Mining
A tradeoff analysis evaluating different fleet size equipment has been completed. Results indicate that the mine can accommodate different truck and shovel options, ranging from 150 ton to 50 ton trucks, with varying impacts on CAPEX and OPEX. Final selection of fleet equipment is expected in the third quarter of 2017.
Infrastructure
Basic engineering for the infrastructure is being updated to reflect changes from the optimization in mineral process design, project layout, and economic parameters in Argentina since the publication of the Feasibility Study in early 2016.
