Increased Metallurgical Recoveries

RNS Number : 7150F

Hummingbird Resources PLC

29 April 2014

 



29th April 2014

Hummingbird Resources plc

("Hummingbird" or the "Company") (AIM: HUM)

Increased Metallurgical Recoveries for Tuzon Deposit

Hummingbird Resources, the Liberian gold exploration and development company, announces results of extensive metallurgical test work carried out as part of its Detailed Feasibility Study ("DFS"). 

Highlights

·     Increased recovery rates across the Tuzon deposit

·     90% recoveries at Tuzon, up from 88% in the PEA

·     Cyanide consumption reduced from 0.9 kg/t to 0.3 kg/t as a result of lead nitrate addition

·     75 micron grind sized for plant confirmed as optimum trade off of recovery against power costs

·     Mining dilution included in all samples to yield expected mill feeds

·     Recoveries a significant driver of improved project economics

Dan Betts, CEO of Hummingbird Resources said:

"Improvement to recovery in the metallurgical test work marks another important step in our optimization of the project and progress towards completion of the DFS.  Building on the work done for our PEA we are very pleased that following further comprehensive test work an increase in recoveries to 90% across the Tuzon deposit has been achieved.  The Company remains fully funded beyond DFS."

Metallurgical Test Work Development

PEA Test Work

As part of the PEA completed in April 2013 Wardell Armstrong International, (on behalf of the Company), completed standard bottle roll tests on 356 assay pulp composite samples from Tuzon showing average gold recoveries of 88.3%. 

DFS Test Work - Phase 1

Phase 1 of the DFS metallurgical test work was completed in Q4 2013.  This was focussed on flow sheet selection comparing the following alternatives;

·     gravity concentration;

·     flotation concentration,and;

·     conventional Carbon in Leach ("CIL") processing

The work was carried out by Mintek and Gravity Concentrators Africa in South Africa utilising a composite  prepared from carefully selected crushed drill core samples from across the Tuzon deposit.

The composite was split into two portions. One portion with Mintek was split into sub-samples for head grade determination, grind curve determination, diagnostic leaching and flotation test work. The second portion was utilised for gravity concentration test work at Gravity Concentrators Africa. 

The results confirmed that direct CIL of ore milled to 80% passing 106 micron, yielded higher overall recoveries than either pre-concentration method, even if followed by CIL of tailings from the pre-concentration step.

The above work confirmed the flow sheet as SAG/Ball milling, followed by CIL, with all further test work focussing on this process route. 

DFS Test Work - Phase 2

Phase 2 of the test work was completed in Q1 2014 following the Phase 1 process flow sheet.  Phase 2 work had two primary objectives;

·     determining the grind size, where the cost of milling against gold recovery is optimised; 

·     metallurgical mapping to better understand the variability across the deposit.

In addition, trade off studies were conducted to evaluate additions to the process flow and hence improve recoveries.

Sample selection was based on geographic location within the proposed pit area.  Mining dilution was included in all of the samples to yield expected mill feed grades. The key findings can be summarised as follows;

·     Diagnostic leach tests indicated that 9-11% of gold was associated with sulphide minerals leading to a decision to evaluate lead nitrate as a potential catalyst for gold leaching.  Lead nitrate acts in two ways; lead occupies sites on gold particle surfaces preventing passivating sulphur coatings and secondly the rate of the oxygen reduction reaction is increased which determines the overall rate of gold dissolution. 

·     Tests were carried out at 50, 250, 500 and 1,000 mg/l lead nitrate with a consistent increase in gold extraction with additional lead nitrate. The addition of lead nitrate was also found to yield a significant reduction in cynanide and lime consumption.  Notably cyanide consumption was reduced by 67%  from 0.9kg/t to 0.3kg/t.

·     The test work led to the selection of a grind size of 75 micron.  Gold recovery shows an increasing trend with fineness of grind from 150 micron to 75 micron. 

·     The variability tests yielded recoveries ranging from 86.3% to 93.5% with average recoveries of 90% for sulphide samples and 92% for oxide samples.  The oxide portion of the deposit makes up less than 10%.    

Ongoing Test Work

To further optimise the metallurgy of the Tuzon deposit ongoing test work is focussing on;

·     Testing pre-oxidation and CIL at elevated oxygen levels to see if this yields similar results to the lead nitrate addition at lower cost;

·     Testwork to optimise the addition rate of lead nitrate;

·     Testwork on the use of alternative oxidants and sources of nitrate to reduce costs compared to lead nitrate;

·     Settling testwork to determine final thickener sizing.

The above optimisations will be included in the DFS if they offer superior recoveries or technical or economic benefits over the existing selected process.

Note: David Pelham has reviewed and approved the technical information contained within this announcement in his capacity as a qualified person, as required under the AIM rules.  David Pelham is a Director of the Company and is a member of the Institute of Materials, Minerals and Mining.

ENDS

Enquiries:

Hummingbird Resources plc

Daniel Betts, Chief Executive Officer
Thomas Hill, Finance Director
Robert Monro, Head of Business Development	[phone]
Cantor Fitzgerald Europe
Nominated Adviser and Broker
Stewart Dickson / Tom Sheldon / Jeremy Stephenson	[phone]
FTI Consulting LLP
Financial PR
Ben Brewerton / Oliver Winters / Sara Powell	[phone]

Notes to Editors

About Hummingbird Resources Plc

Hummingbird Resources plc is an AIM quoted mineral exploration company incorporated in England and Wales and headquartered in London. Since its establishment in November 2005, the Company and its subsidiaries (the "Group") has been active in Liberia, West Africa, and is currently the holder of the largest area of mineral exploration ground in the highly prospective Birimian geological region of eastern Liberia. The Group has published a PEA on its project showing that using a $1,500 gold price,  on a 3.5Mtpa tank leach operation, The project has an NPV of US$337m on a Capex of US$212m for an IRR of 43.4%. This gives a payback period of 3 years and is based on a 10% discount rate and US$1,500 gold price (three year average gold price at time of release).

The Group has recently published a Mineral Resource estimate for the Tuzon deposit constrained within a US$1,500 pit shell and using a 0.5 g/t cut off grade comprising of an Indicated Resource of 41.8 Mt at an average grade of 1.51 g/t Au for 2.03 Moz of gold and an Inferred Resource of 10.2 Mt at an average grade of 1.32 g/t Au for 0.43Moz of gold in accordance with the Canadian Institute of Mining, Metallurgy and Petrology Definitions Standards ("CIM Code") for Reporting of Mineral Resources and Ore Reserves.  The Group has also published a NI43-101 compliant Inferred Resource on its Dugbe F deposit of 43.01 million tonnes at 1.28 g/t Au to give 1,764,000 ounces of gold using a lower cut-off grade of 0.5 g/t Au and no upper cut-off grade.

For more information, please visit www.hummingbirdresources.co.uk

 

END

 

 

MSCIPMBTMBITTJI