Chesapeake Gold Corp. (TSXV: CKG) has provided a metallurgical update for its world class, Metates gold-silver project located in Durango State, Mexico.
Metallurgical Testwork Program – Initial Column
The sulphide heap leaching metallurgical test programme commenced in May 2021 with a sample that had already been crushed to ½” and stored in Denver for several years.
The sample was placed in a transparent column for the oxidation phase. The column was run for 128 days and achieved an oxidation of approximately 30%. After the oxidation phase, the column was rinsed and then leached with a standard lime cyanide solution. The leach cycle was run for 90 days, similar to a standard oxide gold heap leach test.
Over the 90-day leach period, gold recovery reached almost 60% and silver recovery just over 50%. These results are extremely encouraging as they show significantly higher precious metal recoveries than unoxidised samples from previous test work used to support the 2013 and 2016 prefeasibility studies (PFS).
Phase 1 – Oxidation Testwork
With fresh drill samples, an extensive metallurgical test program commenced in a Vancouver laboratory. The core material was composited into two bulk samples. One for the Massive Intrusive mineralisation and one for the Intrusive Breccia mineralisation. These two rock types represent the higher-grade core mineralisation and have been the focus of the testwork program to date.
The initial tests were all run under the same conditions and were aimed at developing time vs’ oxidation vs’ gold and silver recovery curves for both the Massive Intrusive and Intrusive Breccia. Two columns were also run with NO pre-oxidation to determine a baseline “Zero” oxidation gold and silver recovery. The oxidising columns were run for 60, 120 and 180 days.
With no pre-oxidation the two mineralization types tested returned approximately 35% gold and 20% silver recoveries. The initial intrusive column demonstrated higher recoveries with almost 60% gold recovery and over 50% silver recovery. Higher recoveries above these levels are generally a successful indication that the mineralization when oxidized will give better recoveries in a heap leach environment.
Concurrently, an additional 12 columns were run at the same time as the “Zero” column testing using two different alkaline oxidation chemistries. These columns generally gave good repeatability in the oxidation rates when the columns were run under exactly the same conditions.
The oxidation rate, however, when compared to the first sample tested was slower and did not reach a similar oxidation level.
“The metallurgical results to date confirm that the fresh core samples being tested from Metates will oxidise in a similar fashion to the first column. We are now focusing on optimizing the oxidation rate and achieving sufficient oxidation to achieve the targeted gold and silver recoveries,” President and CEO, Alan Pangbourne, said.
Phase 2 – Variable Testwork
A second round of testing is underway and is designed to investigating ways to speed up the oxidation kinetics and have multiple columns running under various conditions to improve and optimise the oxidation rate.
The variables being tested includes crushing finer to ¼”, using High Pressure Grinding Rolls (HPGR) to crush finer, different reagent strengths, different pH’s, on/off irrigation, and varying air addition rates. Initial oxidation response from some of these changes are encouraging and show higher initial oxidation rates.
Despite the slower oxidation rate of the fresh core samples, Chesapeake remains optimistic that we will be able to optimize and accelerate the oxidation to achieve the desired recoveries.
Natural Oxidation – Metates Core Samples
Over the time since the company started the drilling early 2021, it has observed that the Metates mineralisation will oxidise naturally when exposed to air and moisture.
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