Aureus Mining Inc. Metallurgical Testing at Ndablama (3131D)

TIDMAUE

RNS Number : 3131D

Aureus Mining Inc.

28 January 2015

28 January 2015

Aureus Mining Inc.

TSX : AUE

AIM : AUE

EXCELLENT GOLD RECOVERIES CONFIRMED BY FURTHER METALLURGICAL TESTING ON NDABLAMA ORE

Aureus Mining Inc. ("Aureus Mining" or the "Company") is pleased to announce metallurgical optimisation testwork results from its Ndablama Gold project ("Ndablama"), located within the Northern Block of the Company's 100% owned Bea Mountain Mining licence in Liberia, and situated 40 km north-east of Aureus' flagship New Liberty Gold project. The results follow the announcement on 1 December 2014 of an updated Indicated resource of 386,000 oz at 1.6 g/t gold and Inferred resource of 515,000 oz at 1.7 g/t gold. These results confirm and expand upon previous testwork results published on 10 December 2013.

The tests were performed by ALS laboratories in Perth ("ALS"), Australia, under the supervision of DRA Mineral Projects (Pty) Ltd ("DRA"). They were conducted on bulk composite samples from Ndablama drill cores to test the metallurgical response of the oxide and high grade ("HG"), medium grade ("MG") and low grade ("LG") sulphide material composites to standard gravity and cyanide leach treatment routes. The following key results are highlighted:

Highlights

-- Testwork results for the sulphide composites gave overall gravity plus Carbon in Leach ("CIL") gold recovery of between 91% and 96% from head grades of 1.4 to 2.7 g/t gold.

-- The oxide ore gave overall gravity plus CIL gold recovery of between 96% - 97% from a head grade of 0.8 g/t gold.

-- Sulphide ore total gravity gold recovery ("GRG") on the various composites gave test work recoveries of between 66% and 72%.

-- Flotation testwork showed gold recoveries of in excess of 90% into the flotation concentrate.

-- Optimisation of processing parameters indicated low cyanide consumptions of between 0.26 and 0.40 kg/t for standard gravity and CIL extraction.

-- These results confirm and expand on the earlier test work reported on 10 December 2013 where gold recoveries following a cyanide leach ranged between 92% and 94% for the oxide and sulphide material.

-- Comminution test work returned a Bond Rod Work index ("BRW(i) (") ) value of 13 kWh/t, a Bond Ball Work index ("BBW(i) (") ) value of 18.5 kWh/t and a Bond Abrasion index ("BA(i) (") ) of 0.1338 with the material being considered to have relatively low abrasiveness. The BBW(i) value is identical to the average outlined for New Liberty.

Commenting on the metallurgical results, David Reading, President and Chief Executive Officer of Aureus Mining Inc., said:

"The detailed metallurgical test work from Ndablama highlights excellent results delivering significant high recovery rates from both gravity and CIL treatment. With these results we are now looking at both standalone and concentrate transport options for the treatment of Ndablama ore. Further exploration work is also warranted as we have only drill tested one kilometre of a thirteen kilometre gold belt. This work further supports the fact that Liberia is a new and emerging gold district in West Africa."

Ndablama Background

The Ndablama gold target is located within the Northern block of the Company's 457 km(2) , 100% owned, Bea Mountain Mining licence in Liberia, and is situated approximately 40 km north-east of Aureus' flagship New Liberty Gold project. A total of 115 diamond drill holes covering 21,333 m, 39 reverse circulation ("RC") infill holes totalling 5,827 m and 63 trenches for 3,967 m have been completed at the Ndablama gold target and span 1.7 km of a northerly striking mineralised system. A resource estimation comprising at a 0.5 g/t cut off a total of 386,000 oz at 1.6 g/t gold indicated and 515,000 oz at 1.7 g/t gold inferred has been calculated based on drill holes covering a strike length of 1,000 m (150 drill holes and 26,689 m) of the mineralised system. It comprises effectively the Central, South East and an area of the North zone of the deposit while the mineralisation remains open along strike and down dip.

Work completed

Subsequent to the initial test work programme (published on 10 December 2013), further optimization test work was conducted at ALS Laboratories in Perth, Australia. At the request of the Company, the test work was scoped and managed by DRA with the aim of confirming the initial test work results and to determine optimum design parameters.

Representative samples of oxide and sulphide material were selected by the Company geologists and dispatched to ALS. A total of 694 kg of material was received by ALS and composited for comminution work at JKTech, gravity work at ConSep and gravity / cyanidation work at ALS.

For the ALS work, bulk composites of the sulphide material were constructed to characterise typical low, medium and high grade material with head grades of 1.40 g/t, 1.83 g/t and 2.70 g/t of gold for the respective composites. A representative oxidised bulk composite was also constructed with a head grade of 0.82 g/t gold.

Testworks Outcomes

Results are presented for testwork on composite samples made up from 47 diamond drill holes (630 metres) from all phases of the drilling programme completed at Ndablama.

Head grades of the samples

-- The head grades of the various composites generated for the testwork programme are indicated in Table 1;

Table 1: Composite head grades

 
             Sample                 Au 
                                   (g/t) 
-------------------------------  ------- 
 Oxide ("OX") composite            0.82 
-------------------------------  ------- 
 Low Grade ("LG") composite        1.40 
-------------------------------  ------- 
 Medium Grade ("MG") composite     1.83 
-------------------------------  ------- 
 High Grade ("HG") composite       2.70 
-------------------------------  ------- 
 

Evaluation of CIL recovery as a function of grind size

-- Grind optimisation testwork was conducted on the HG composite and indicated that the optimum grind is P(80) of 75mm with a residue grade of 0.14 g/t Au and an associated total extraction of 95.3%. This grind size returned the optimum combination of high extraction with low associated reagent consumption.

Evaluation of gold recovery to flotation concentrate

-- Flotation testwork was performed on the composite samples with gold recoveries in excess of 90% into the flotation concentrate.

Evaluation of gold recovery by gravity separation

-- Testwork was conducted on the LG, MG and HG composites returning maximum total gravity recoverable gold (GRG) values of 68.0%, 71.7% and 66.1% respectively;

-- Gravity separation tests on the oxide composite were performed at ALS Laboratories and yielded non-discounted recoveries ranging from 41% - 43% for gravity recoverable gold (GRG).

Evaluation of preg-robbing

-- The testwork showed that gold extraction was similar for tests conducted with carbon present compared to leach tests conducted with no carbon present as per Table ;

-- Based on the similarity in overall extraction it can be inferred that there is no evidence of preg-robbing.

Table 2: Preg-robbing testwork results

 
  Sample     Grind     Carbon    Leach residue grade   Total extraction 
              size     at time          (g/t)                 (%) 
              P(80)     (hrs) 
----------  -------  ---------  --------------------  ----------------- 
 HG comp.     75mm       0              0.12                95.64 
----------  -------  ---------  --------------------  ----------------- 
 HG comp.     75mm       4              0.14                94.71 
----------  -------  ---------  --------------------  ----------------- 
 HG comp.     75mm      None            0.12                95.84 
----------  -------  ---------  --------------------  ----------------- 
 OX comp.     75mm       0              0.03                96.34 
----------  -------  ---------  --------------------  ----------------- 
 OX comp.     75mm       4              0.03                97.04 
----------  -------  ---------  --------------------  ----------------- 
 OX comp.     75mm      None            0.03                96.46 
----------  -------  ---------  --------------------  ----------------- 
 

Evaluation of the effect of pre-oxygenation with shear

-- No significant benefit was observed in terms of total extraction, cyanide consumption or lime consumption when pre-oxygenation was included in the test. The total extraction shown in Table 3 with pre-oxygenation is very similar to the total extraction realised without pre-oxygenation.

Table 3: Pre-oxygenation testwork results

 
  Sample     Grind    Leach residue   Total extraction   NaCN consumption 
              size        grade              (%)              (kg/t) 
              P(80)       (g/t) 
----------  -------  --------------  -----------------  ----------------- 
 HG comp.     75mm        0.17             93.69               0.56 
----------  -------  --------------  -----------------  ----------------- 
 

Optimization of cyanide consumption

-- Cyanide optimisation tests were conducted on the MG composite at the target grind of P(80) of 75mm with results showing that there was an optimum cyanide consumption of 0.43 kg/t with a leach residue of 0.13 g/t Au.

Evaluation of gold recovery from leaching of the oxide feed material

-- Tests conducted on the OX composite at the target grind of P(80) of 75mm resulted in leach residues of 0.03 g/t Au, yielding total gold extractions ranging from 96.3% - 97%. Cyanide consumptions varied between 0.25 kg/t and 0.75 kg/t.

Flowsheet validation

-- Once the optimum processing parameters of grind size, cyanide consumption and pre-oxygenation with shear had been identified, a series of tests was conducted to validate these parameters.

-- The purpose of this work was to test the consistency of the results with the proposed flowsheet on the sulphide composites (Table 4).