Metallurgical testwork confirms Wiluna transitional reserves amenable to processing through the existing Wiluna CIL plant
Testwork Confirms Transition Ores Amenable to CIL Processing
- Expansion PFS published in Aug'17 includes a significant proportion of oxide and transitional probable reserves
- Expansion PFS conservatively assumed the transitional ores would be processed through the sulphide plant
- Further metallurgical testwork on the Wiluna transitional ores has averaged 84.3% Carbon In Leach (CIL) metallurgical recovery
- Testwork results from the Wiluna transitional ores are consistent with these ores mined and processed prior to 1993 when the Sulphide circuit was commissioned
- Testwork confirms the transitional ores can be processed in the Wiluna CIL plant at a lower cost and improved recoveries in comparison to the sulphide plant
- The Wiluna transitional ores tested have an expected average CIL recovered grade of 1.77g/t.
During March'18, Blackham's exploration team drilled 84 RC holes (6,491m) focused on delineating further free milling open pit reserves over the 4km's of strike at the Wiluna Mine. Initial results from this drilling are due to be released shortly. This was a follow up programme on the 77,000m of drilling completed during 2017, which successfully delivered probable reserves of 669,000oz (7.7Mt @ 2.7g/t Au), and included oxide, transitional and fresh reserves. The current drilling is focused on free milling ores above the top of fresh rock (generally top 60m) which metallurgical testwork has confirmed are best processed through the current Wiluna CIL plant rather than the sulphide circuit.
Wiluna mining and metallurgical studies are well advanced in this area following the successful Wiluna Expansion Preliminary Feasibility Study (Expansion PFS) published in August'17. The latest testwork confirms the Wiluna oxide and transitional ores are an attractive feed stock for the current operating Wiluna CIL plant. All of the historic open pits were processed through the Wiluna CIL plant with the exception of the 2007 East pit cut back. Blackham is currently re-estimating the open pit free milling reserves within the Wiluna Mine footprint.
During 2017, Blackham completed 77,000m of RC and Diamond drilling used in completing the successful Expansion PFS. All of these drill holes have been assayed for gold, sulphur, sulphide and arsenic. The fresh (refractory) ores at Wiluna have significantly elevated As and S which can be seen in Table 1 (see link below). The As, S and SO2 analysis has been used to remodel both the base of oxidisation (BOCO) and top of fresh surfaces from a metallurgical view point to accurately define the free milling ore zones.
Metallurgical testwork on both the oxide and transitional ores has confirmed that these ores are best processed through the current CIL plant. In the Expansion PFS it was conservatively assumed that the transitional ores would be processed through the Flotation and Biox(R) Plant (Sulphide Circuit). Not only does the transitional ore gain higher recoveries through the CIL plant, the processing cost is approximately 30% less than the sulphide circuit.
Average leach recoveries on the oxide ores were 90.8% after 24 hours with little increase in recovery after that. Bond ball mill work index tests on the oxide ore range from 10-14 kWh/t. Gravity gold recoveries were low ranging from 1.3-9.8%. Cyanide consumption results were low to moderate ranging from 0.14-0.23kg/t over 24 hours. Lime consumptions were low range from 0.6-1.4kg/t over 24 hours.
Average leach recoveries on the transitional ores were 84.3% (see Table 2 in link below). Cyanide consumption results were low to moderate ranging from 0.14-0.20kg/t over 24 hours. Lime consumptions were low range from 0.7-1.3kg/t over 24 hours. Bond ball mill work index tests on the transitional ore range from 16-19 kWh/t. Follow up drilling has now been completed to obtain additional transitional ore samples for the next round of metallurgical testwork.
Blackham is currently re-estimating the open pit free milling resources and reserves around the Wiluna Mine site. The Blackham management team believes the free milling ores within the existing Wiluna Mine footprint are an attractive feed stock for the current operating mill and allows for fast tracking mining approvals.
To view tables and figures, please visit:
About Blackham Resources Ltd
Blackham Resources Limited (ASX:BLK) (OTCMKTS:BKHRF) Wiluna-Matilda Gold Operation is located in Australia's largest gold belt which stretches from Norseman through Kalgoorlie to Wiluna. The Operation now includes resources of 96Mt @ 2.2g/t for 6.7Moz Au all within 20kms of the central processing facility. Blackham has consolidated the entire Wiluna Goldfield within a +1,440km2 tenure package which has historically produced in excess of 4.4 million ounces over a 120-year mining history.
Blackham Resources Ltd