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Filo Mining Announces Positive Metallurgical Testwork Results from Filo del Sol Deposit

Filo Mining Corporation ("Filo Mining" or the "Company") is pleased to report positive results from an initial program of metallurgical testwork on oxide mineralization from the Filo del Sol deposit. Testwork was completed by SGS Canada Inc. in Lakefield, Ontario under the supervision of Dr. Joe C. Ferron who is a consultant to the Company.

Bottle-roll tests were completed on reverse circulation (RC) drill cuttings of three separate types of mineralization representing three distinct zones within the deposit. The results are summarized below:

Zone Head Grade Recovery
Oxide Copper (CuOx) 0.33 gpt Au; 0.44% Cu 95.1% Copper
Oxide Gold (AuOx) 0.49 gpt Au; 0.02% Cu 93.2% Gold
Mixed Silver (M) 0.34 gpt Au; 0.29% Cu; 103 gpt Ag 88.6% Gold; 92.4% Copper; 92.7% Silver

Key results from this initial test program were that the metallurgy of the AuOx mineralization appears totally problem-free and that the CuOx mineralization also appears straightforward, with copper being almost completely soluble. The metallurgy of the M zone mineralization indicates good extractions of silver, gold and copper by cyanidation, but at the expense of high cyanide and lime consumption. The M zone mineralization will require additional work to determine the optimum processing solution.

Bottle roll tests are used to determine whether metals can be recovered by heap leaching, and provide a good indication of maximum expected metal recoveries. Heap leaching is a widely used processing method for recovering metals from oxidized mineralization and typically involves lower capital and operating costs than the flotation process that is used for sulfide material.

In addition to the tests above, a sequential leach test was done on the CuOx sample. Sequential leach involves acid leaching of the material to recover copper, followed by thorough rinsing, neutralisation and cyanide leaching to recover gold. It offers the potential to recover both copper and gold from the CuOx material. The sequential leach test provided 94% copper recovery and 87% gold recovery, indicating that it is a processing method that warrants additional testwork in order to determine if it might be applicable on a project scale.

"These results are very encouraging," commented Wojtek Wodzicki, President and CEO of Filo Mining. "and support further evaluation of the potential to heap leach the upper part of the Filo del Sol Deposit. We are particularly impressed by the fast leach times and the indications that the Oxide Copper zone may be amenable to leaching with plain water rather than sulfuric acid. The excellent gold recoveries obtained from sequential leaching of copper and then gold from the oxide copper material is also very positive and suggests that recovery of gold from the oxide copper zone may be possible."

Bottle roll leach results for the CuOx material indicated that the copper was very soluble and no acid was needed to obtain a target pH < 2.0 suggesting the material may be amenable to simple water leaching. Leach kinetics were excellent with ultimate copper extraction of 95.1% achieved in approximately 24 hours.

Bottle roll cyanide leach results for the AuOx material indicated gold was very soluble, with a recovery of 93.2% achieved after 24 hours when using 1 g/L cyanide concentration. Cyanide consumption was moderate at 0.67 kg/tonne.

Bottle roll cyanide leach results for the M zone material indicated that silver, gold and copper were soluble with recoveries of 92.7%, 88.6% and 92.4% respectively after 96 hours. Cyanide and lime consumption were high, mostly due to the relatively high concentration of copper in the sample. Mineralogical studies completed last year indicated that this zone is comprised of several different silver and copper-bearing minerals and that the mineralogy of this zone is quite variable. Accordingly, it is challenging to obtain a sample which is representative of the zone and the results obtained during this initial test may not necessarily be applicable to the entire M zone.

A key component of the upcoming field program, expected to start in November, will be to collect additional sample material from all three zones in order to complete a more comprehensive test program early in 2017. Coarser sized samples from surface will be collected for use in the column testing which will better approximate the conditions in an actual leach operation. Recoveries from column tests are typically lower than from bottle roll tests.

In addition to completing initial column leach tests, the 2017 program will have two specific goals:

  • Investigate processes which could recover both the copper and gold from the CuOx material. Two methods which will be investigated are sequential leach and Sulfidization, Acidification, Recycling and Thickening (SART). In a sequential leach, material is first leached with acid to recover the copper, then neutralized and leached with cyanide to recover the gold. The SART process allows recycling of the cyanide following the extraction of copper. If successful, either of these methods could allow for the recovery of both the copper and gold from the CuOx material.
  • More fully investigate the M zone material, which is more complex that either the CuOx or AuOx. Additional mineralogy studies will be done in order to better define the variability within this zone, to help select representative samples and to confirm expected process recoveries.

Technical details of the initial bottle roll test results are presented below:

Table 1: Acid Leach Conditions
Test No. Sample Feed Density Time H2SO4 pH Residue Weight Loss
(g) (%) (hours) (kg/t) (g) g %
LC-1 ZC CuOx 252.6 20 96 0.0 1.6-1.7 204.6 48.0 19.0
Table 2: Acid Leach Results
Test No. Sample Cu Copper Assay
Extr'n % Solution (mg/L) Solids (%)
8 h 24 h 48 h 72 h 96 h Residue Calc Feed
LC-1 ZC CuOx 95.1 1050 1050 1070 1060 1020 0.028 0.46
Table 3: Cyanide Leach Conditions
Test No. Sample Feed (g) Density (%) Time (h) NaCN Conc (g/L)
CN-1 ZC AuOx 246 20 2 96 1.0
CN-2 ZC M 263 20 2 96 1.0
Table 4: Cyanide Leach Results
Test No. Sample Extraction Residue Assay Calc Head
CN-1 ZC AuOx 93.2 ~70* 17.6 0.032 <0.05 0.012 0.47 <0.2 0.01
CN-2 ZC M 88.6 92.7 92.4 0.043 8.37 0.020 0.38 115 0.26
* very approximate due to low silver levels in feed

On behalf of the board of directors of Filo Mining,

Wojtek Wodzicki, President and CEO, Filo Mining


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