Ventnor Resources' (ASX: VRX) deep drilling program at its Thaduna and Green Dragon project in Western Australia has intersected up to 13.5 metres at 3.25% copper, supporting depth extensions to the high grade zone below the current resource.
All holes intersected copper sulphide mineralisation including high grade bornite and primary chalcocite within the mineralised zones, confirming the understanding of the sulphide zonation which occurs at the Thaduna deposit.
"This deep drilling campaign of 12 deep diamond holes was aimed at extending the high grade zone at Thaduna and has now confirmed copper mineralisation to a depth of 650 metres," managing director Bruce Maluish said.
"The deeper intersections also confirm widths and grade which are potentially suitable for underground mining. These widths have now been encountered over 400 vertical metres below the Thaduna optimised pit.
"The campaign has been completed and following the receipt of assays we will recalculate the Resource and plan further drilling to delineate the full extent of the mineralisation."
All assays have been received from the deep drilling campaign with check assays underway on higher grades and results expected over the next two weeks with an announcement to follow.
An additional four shallow diamond holes were drilled below the Thaduna pit to provide geotechnical and metallurgical samples.
Metallurgical testwork carried out by ALS Metallurgy under the direction of Met-chem Consulting indicates very high recoveries, concentrate values and ultra-low impurities from Thaduna with indications that recovery is not significantly impacted by a coarser upfront grind and that a simple low cost reagent is required.
Ventnor continues to evaluate a number of equity, equity/offtake, equity/debt, equity/JV and JV proposals and expects to finalise an agreement in the coming weeks.
Drilling to date at Thaduna comprises 221 reverse circulation holes for 29,041 metres with 72 Diamond Tails for 17,374 metres, totalling 46,415 metres.
THDD226, which returned an assay of 13.5 metre at 3.25% copper from 520 metres, was one of the early holes drilled as part of this program.
It intersected a strong wide graphitic zone with bornite, chalcopyrite and chalcocite sulphide mineralisation present with all assays within the interval returning at least 1% copper.
The wide intersection shows a distinct grade variation with higher grades associated with the hangingwall and footwall contacts within a +3% envelope.
The hangingwall position averaged 3 metres at 4.24% copper and the footwall position averaged 4.27 metres at 4.07% copper.
It is interpreted that the Thaduna mineralisation splits between a single structure and two structures and THDD226 has intersected close to the bifurcation point and thus the wide zone with two distinct higher grade zones.
Three phases of testwork have been completed.
The initial program was to determine the amenability of the ore to flotation, the optimum grind size and appropriate reagents. The second program was a more detailed test at the varied grind sizes over different vertical geological zones. The third test program was to test the amenability of the shallow zones to leach testwork.
Rougher optimisation test work to date suggests that a fine grind is not necessary with a 75μm grind size yielding 91.9% recovery while a finer 45μm resulted in 93.2% recovery.
It has also been determined that although the mineralogy responds well to expensive flotation reagents, comparable results were achieved with cheaper xanthate based collectors.
The combination of these two parameters will result in significant operating cost savings.
Leach testwork near surface has also been completed which indicates that near surface ore is also amenable to leaching with a recovery of between 60% to 90%, down to a depth of 70 metres where chalcocite becomes the dominant copper source.
This has found that while there are some oxide copper minerals near surface there is a predominance of copper sulphide minerals which are very amenable to flotation.
It is planned to undertake further sequential copper analysis on the laboratory pulps for all intersections above 200 metres vertically at both Green Dragon and Thaduna. This will result in better metallurgical modeling for the Bankable Feasibility Study.
Future BFS work will include diamond drilling to gain samples for additional metallurgical testwork.
This will target near surface positions to be able to better define the treatment route of ore mined from a potential open cut. Flotation optimisation testwork will be focused refining the following parameters:
- Rougher grind size: Work to date indicates recovery is not significantly impacted by a coarser upfront grind;
- Cleaner grind size: All cleaner tests to-date have been re-ground to 20μm. If regrinding is not required it will result in operational and capital cost savings; and
- Definitive reagent suite: Work to date has identified that a simple low cost reagent suite is required.
Thaduna/Green Dragon is located in the Doolgunna district of Western Australia and has a current Resource of 142,000 tonnes of contained copper and 945,000 ounces of contained silver.
A Bankable Feasibility Study is currently underway and is scheduled for completion in the September quarter 2013.
This will focus on detailed mine planning, metallurgical testwork, processing options, confirmed contract rates and operating cost reduction initiatives.
The Scoping Study completed in February had indicated the project will deliver attractive economics with capital expenditure estimated at $70 million and the average operating expenditure expected to be around $1.75 per pound.
This is based on a mine that will produce 15,000 tonnes of contained copper per annum over a 10 year mine life, with high recoveries and concentrate value.
The extension of the high grade copper zone below the current Green Dragon and Thaduna resource is a positive for Ventnor Resources, giving it the option to expand the project beyond the original open pit with underground mining.
Testwork has also been encouraging with indications that regrinding may not be necessary for good recoveries. This and the requirement for a simple, low cost reagent, will result in cost savings for the project, increasing its attractiveness.
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