RE:News - Processing TestsHigh and Fast Gold Recoveries
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After expanding its exploration footprint (~25%) to 48.5 square kilometers to
accommodate some new discoveries at the Black Pine oxide gold project in southern Idaho,
the company has released results from the Phase 1 metallurgical testwork,
which is another critical catalyst to proving the viability of a potentially multi-million-ounce,
heap leach amenable open-pit deposit.
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The company reported gold recovery results from six bulk tonnage samples from several
zones to add to the database of testwork conducted by Noranda back in 1988.
The new testwork was reviewed by Gary Simmons, who used to be the Director of Metallurgy
and Technology for Newmont Corp. (NEM.NYSE, NGT.T) and played a similar role for
Fronteer Gold on the Long Canyon gold mine.
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Metallurgical testing is used to identify the ultimate metal recovery and the cost of
processing, which is a function of the size fraction chosen and the amount of time required
to leach the gold from the refractory ore.
A lengthy recovery process is the main reason many companies with a single heap leach project tend to have cash flow issues since they may have to wait months for the revenue to be recognized.
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### Overall, there is a good correlation between gold grade and its recovery.
One exception is the I Pit sample, which had a head grade of 2.67 grams per tonne gold,
but the recoveries were lower than the Tallman Pit’s sample, which had a lower
grade of 2.1 grams per tonne gold.
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There is no carbonaceous material in the sample;
therefore, it may be an issue with gold encapsulated in silica since the fine fraction (75 microns)
generated a recovery of ~75%, almost 15% better than the run-of-mine column test.
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The results are similar to one of Noranda’s samples from the B-Pit (Core BP-87-73C),
which also had a significant delta (10-15%) between the gold recovery from the fine fraction sample versus the coarser ones.
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### The highest recovery should be from the finest fraction (75 microns or less),
but in many samples, the difference with the coarsest fraction is negligible.
The recovery from the column test of a sample from the C/D pits was actually
higher for the run-of-mine fraction (76.8%) than the fine fraction (64.6%),
which is rather strange.
Note that the leaching time for the fine fraction was only a few days compared to 100 days for the run-of-mine.
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### Testwork so far suggests that the vast majority of the gold from all the samples,
regardless of final recovery,
is recovered in the first 20 days of the testing, which is positive.
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Overall, the first phase of the detailed metallurgical testwork at Black Pine suggests the
potential to achieve excellent recoveries that average 78% (up to ~88%) in a short time
frame (20 days) from the coarse run-of-mine fraction.
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In the end, a combination of run-of-mine and selective crushing may be the path forward.
This variation should be built into the cut-off grades for the resource models since the
processing costs for the former are much less than the latter.
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The second phase of metallurgical testwork will be more detailed, with 29 composites
(versus 6 in Phase 1) sampling the different stratigraphic units, structures, alteration halos,
and grades.
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Liberty has covered the Black Pine area enough to protect it from competitors.
In addition, the company is currently engaged in an up to 45,000-meter drill program (3-4 rigs) to follow up on two discoveries from 2019.
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Acknowledgment: Exploration Insights Newsletter - Joe Mazumdar & Brent Cook - 06/21/2020
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RJ