Blackham Resources Ltd: Wiluna Tailings (Wiltails) - Maiden Resource
24.07.2018 | ABN Newswire
Perth - Blackham Resources Ltd. (ASX:BLK) (OTCMKTS:BKHRF) (Blackham or the Company) is pleased to provide an initial Mineral Resource estimate for the historical tailings at the Company's Wiluna Gold Operations all within 2km of the Wiluna processing plant. The historical tailings have accumulated at the site since the 1930's and recent independent metallurgical test work has shown that potential gold recoveries of between 42-50% can be achieved through standard mining and gold leaching processes. Additional metallurgical test work will potentially enhance the gold recovery and validate how this material may supplement the Company's operating plans.Highlights
- 620,000oz added to Wiluna free milling gold Mineral Resource base
- The maiden Mineral Resource for the Wiluna Tailings is 33.6Mt at 0.57 g/t Au. 77% of the Mineral Resource is classified under JORC 2012 as Indicated Resources (see Table 1 in link below)
- Metallurgical test work completed to date indicates a recovery of between 42-50% for the historical tailings in a standard gold leaching process similar to the existing Wiluna CIL circuit.
- Ongoing technical work will be completed on the tailings to confirm potential mining and processing options for possible integration into the Company's future operations.
Blackham has successfully identified additional free milling ore associated with the Golden Age mineralisation and the Wiluna oxidised zones (see announcements "Wiluna High Grade Free Milling Mineralisation Extended" dated 21 June 2018 and "Multiple High-Grade Extensions Identified at Golden Age" dated 12 June 2018).
The Company also continues its exploration programs into its priority Lake Way targets and has now completed the first phase of drilling. This drilling is the first new drilling in that area for 12 years and the Company is awaiting final results.
Blackham will continue to add to its free-milling resource inventory at its Wiluna operations with a view to fully utilising its available assets and increasing shareholder value. Annual updated Mineral Resource estimates are currently underway for all areas at Wiluna and will be reported in the current quarter.
Mineral Resource Estimate
Tailings material has been deposited since the 1930's around the Wiluna processing plant from over 4.4Moz of gold production. Since the mid 1990's both purpose built tailings storage facilities (TSF) and open pit voids have been utilised. The tailings being deposited from current operations into Storage Dam J is not included in this resource.
Resources were estimated by Blackham personnel for the various tailings impoundments using historical data and the data from two recent drill campaigns.
A significant proportion of the tailings resulted from processing of the Wiluna UG sulphide ores through the Biox(R) plant with historic processing records indicating an average tailings grade of 0.72g/t over the last 13 years. This was deposited into all of the above locations except Dam C which was the first storage location. Recent metallurgical testing has indicated that further recovery of the residual gold is possible through the oxide milling circuit. Two recent drill programmes have enabled sufficient data to estimate the grade for the separate repositories.
The separate tailings storage areas are:
- Dam C - largest single resource. The material is layered with the upper part resulting from processing of sulphide ore (~40%) and the lower part from oxide ore treatment.
- Dam H and the Western Extension of Dam C. Both containing residue from sulphide ore treatments.
- Pits - Adelaide, Golden Age, Moonlight and Squib. All containing residues from largely sulphide ore treatment. (Tailings have also been placed in the Gun Barrell Pits, North and South, - these potential resources have not yet been tested.)
The Mineral Resource has been classified as Indicated (77%) and Inferred in accordance with the JORC Code, 2012 Edition on a qualitative basis taking into consideration numerous factors including drill hole spacing, estimation statistics and sample data. All factors that have been considered are detailed below or included in the Appendices. There have been no prior estimates for this material.
Project Location
The Wiltails resource base is located on the Wiluna mine site within approximately 2km of the operating CIL processing plant at the northern end of the Norseman-Kalgoorlie-Wiluna gold belt 600km north of Kalgoorlie.
Geology and Geological Interpretation
The tailings material has been derived from the treatment of the ores around the Wiluna mine area. The mineralisation is shear hosted typical of Archean gold deposits. Rock types range from sedimentary rocks and Felsic to Mafic volcanics. Gold is contained in quartz vein and in alteration zones. In un-weathered rock the mineralisation is commonly associated with sulphides such as pyrite and arsenopyrite.
Processing records indicate that the majority of the tailings were emplaced during the treatment of fresh sulphide rich ores. The notable exception is the material in the bottom part of Dam C that contains primarily oxide and transitional ore residues from the mining of the Wiluna open pits between 1985 and 1997.
Drilling and Sampling Techniques
Two recent drill campaigns were completed over the Wiluna tailings. An initial programme of rotary auger drilling in 2017 tested:
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Prospect Total Number of Holes Total Metres Drilled
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Squib 2 40
Adelaide 2 40
Moonlight 1 20
Golden Age 2 40
Western Cell 3 49
Dam H 16 286.5
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Totals 26 475.5
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The holes were drilled vertically with most holes 20m long to the base of the TSF. Holes were sampled by removing material from the auger at 5m intervals. Only the 16 holes drilled in Dam H were used in the resource estimation.
A second programme of AC drilling was drilled on a nominal 100mx100m grid with a total of 63 holes for 1,576m completed in June 2018. The holes were drilled vertically and varied in length to reach the base of the TSF or pit being assessed. Holes were sampled in 2m intervals.
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Prospect Total Number of Holes Total Metres Drilled
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Squib 8 218
Adelaide 4 78
Moonlight 6 165
Golden Age 6 146
Dam H 8 120
Western Extension 6 105
Dam C 25 744
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Totals 63 1,576
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The six holes drilled in Dam H were not used in the resource estimation owing to sample contamination caused by overlying calcined tailings stockpiles.
Sample Analysis Method
Samples from both programmes were assayed for gold using a 50g charge fire assay by independent certified laboratories following standard sub-sampling procedures. Samples from the initial auger drilling programme were further analysed for their metallurgical properties by an independent consultant.
Bulk Density
A further phase of drilling was completed in July 2018 using sonic core drilling aimed primarily at providing bulk density data for use in the resource estimation. Standard Penetration Tests were taken periodically during drilling to obtain density, strength and consolidation characteristics for the tailings. For the current Mineral Resource Estimate a figure of 1.6 t/m3 was assigned as the global dry bulk density.
Estimation Methodology
The volume of the tailings was estimated either within an existing open pit or a tailings storage facility (TSF). Digital terrain models based on final pit surveys conducted prior to the tails deposition were constructed for the open pits with current topographic models being used for the TSF discounting the material being used for building bunds and/or walls of the TSF.
Gold grades were estimated into the model by inverse distance squared using the block model field coding to constrain the estimate. Only samples contained within each individual domain were used for the estimate of that domain. Top cuts were used to cap anomalously high grade data. The stage 2 drill holes (aircore) for Dam H were not used owing to contamination of samples. Any assays that appeared as outliers from the median grade were cut.
The search ellipse was based on considerations of the drill hole spacing and domain geometry. In addition, visual inspection, using tools available in Surpac, were undertaken to assess the pattern of informing sample selection. The search ellipsoid radii ratios were then chosen to provide an optimal sample neighbour selection for estimation. The search neighbourhood radii were chosen to be as small as possible while still fulfilling the requirement of filling all blocks in the estimation domains with estimates. Search ellipse orientations were flat. Some stratification of the tails sediments was observed in the drilling and the grade interpolation attempted to honour this stratification.
One search pass was used to populate blocks allowing for a maximum of 2 samples per drill hole with a maximum of 8 samples per block estimate. The estimate was validated using a number of techniques including but not limited to:
- A visual comparison of block grade estimates and the drill hole data;
- A comparison of the composite and estimated block grades;
- SWATH Plots
Cut-off Grades
No cut-off grade was applied to the resource estimate and it is quoted as a total in-situ resource.
Mineral Resource Classification
The Mineral Resource is classified as Measured, Indicated and Inferred, in accordance with the JORC Code (2012 Edition). A range of criteria were considered when addressing the suitability of the classification boundaries to the resource estimate including:
- Drill hole spacing;
- Quality of dill hole information accounting for type, and sampling technique; and
- Available mining information.
The classification for this model has predominantly being based on the drill hole type and spacing. In resources drilled by Air Core with 4.5" diameter holes with the specialised 'vacuum bit' with at least 100m x 100m on the TSF and 50m by 50m in the open pits an indicated classification was given. Where rotary auger drill sampling was completed an inferred resource was given due to the lower quality of the sampling.
Economic Extraction
A scoping study was competed for the Wiluna tailings retreatment in 2016 by Independent Metallurgical Operations Pty Ltd. The study comprised preliminary metallurgical test work using Dam H tailings data and a review of potential recovery and treatment options for all storage facilities and pits. The options considered produced acceptable financial returns and indicated a potential metallurgical recovery of 42-50% for gold via a whole of ore leach.
Initial test works have confirmed the tailings material is sized between 38-75micron removing the need for further grinding - significantly reducing re-processing costs. The tailings can be treated through the current operating CIL circuit without the need for further milling or concentration, making reprocessing a simple, low cost option.
This resource and scoping study justifies the assumption for eventual economic extraction and treatment of the Wiluna Tailings.
Further feasibility studies are ongoing aimed at:
- Confirming the metallurgical properties and optimal flowsheet;
- Assessing best method of materials handling (mining, dredging or re-pulping); and
- Integration with the existing free milling and planned sulphide operations.
To view tables and figures, please visit:
http://abnnewswire.net/lnk/E5HX0C86
About Blackham Resources Ltd:
Blackham Resources Ltd. (ASX:BLK) (OTCMKTS:BKHRF), is an emerging gold producer focused on its Matilda Gold Project in Western Australia where mining and production is imminent. The Matilda/Wiluna Gold Operation incorporates over 1,000 square kilometres of tenements containing total JORC 2012 resources of 63Mt @ 3.2 g/t for 6.4Moz of gold. These tenements cover around 55 kilometres of strike along the Wiluna Mine Sequence and 10 kilometres of strike along the Coles Find Sequence. The Wiluna Mine and Coles Find Sequence has historically produced 4 million ounces of gold.
All the deposits are within 26 kilometres by existing haul roads of Blackhams recently acquired Gold Plant. With exploration prospects at Mt Poole, Monarch, Carroll Prior, Red Lady, Zenith, Island and Albion in the Lakeway area provides the company with excellent exploration areas for potential future projects.
Contact:
Blackham Resources Ltd.
Milan Jerkovic Executive Chairman
T: +61-8-9322-6418
Bryan Dixon Managing Director
T: +61-8-9322-6418
Jim Malone Investor Relations
T: +61-419-537-714
Chantelle O Sullivan
Media Relations Citadel-MAGNUS
T: +61-8-6160-4900