THE INSIDE STORY: Infill drilling conducted at a silver-copper project in the southern Gawler Craton, South Australia, supported Investigator Resource’s (ASX: IVR) belief that its Paris project is Australia’s best undeveloped silver deposit.
“The infill program completed in late 2016 achieved a significant increase of 26 percent to 42 million ounces of contained silver at a grade of 139 grams per tonne, which is way above any of our peer deposits as far as grade goes,” Investigator Resources managing director John Alexander told The Resources Roadhouse.
“It’s a very robust project.
“With the infill drilling we confirmed the geological model for the project and believe there’s potential to add another 20 percent from an area we now recognise we haven’t drilled, but we’re happy with where the resource now stands, especially with the upgrade which converted 55 percent of our contained ounces to indicated.
“We’ve now got ourselves into a position where we can now move into a pre-feasibility study.”
The component of the recently announced resource – classified as Indicated – largely corresponds with the area of infill drilling and shows a 41 percent increase in grade to 163g/t silver over the 2015 Inferred resource of 8.8 million tonnes at 116g/t silver for 35 million ounces of silver.
The revised resource was independently prepared by H & S Consulting Pty Ltd (H&SC) using the Multiple Indicator Kriging (MIK) method of estimation, considered the most suitable estimation method for the complex mineralisation style of the Paris deposit.
The mineral resource estimates were reported using a silver cut-off grade of 50g/t and were constrained to above the 25 metres relative level (mRL).
As well as the high grades for the open pit development scenario the tonnage grade profiles also offered flexibilities by adjusting the cut-off grades for more ounces at times of higher silver prices; e.g. to 30g/t cut-off for 50 million ounces silver or to higher grades at times of lower silver prices; e.g. to 70g/t cut-off for 6.2 million tonnes at 179g/t silver for 36 million ounces.
The retention of the bulk of the ounces at the high cut-off is a reflection of the robust grade profile for the Paris project.
Investigator discovered the Paris silver resource in 2011 and then developed flow-on discovery opportunities for copper-gold porphyry-style deposit at Nankivel, five kilometres southeast of the Paris project all within the company’s 100 percent-held Peterlumbo Tenement.
The Paris silver deposit is the first solid discovery in South Australia of an epithermal deposit style.
The Peterlumbo tenement is 583 square kilometres in size and located in the pastoral country of the northern Eyre Peninsula district approximately 350 kilometres northwest of Adelaide and 60 kilometres northwest of the town of Kimba.
Anderson said that company would now concentrate on the pre-feasibility study and does not need to go back to drilling Paris at this time.
“The extent of the resource has been pretty well defined and we’ve closed the drilling,” he explained.
“However, having said that there’s lots of exploration potential to add resource to Paris in satellite deposits, in fact Paris may be a satellite deposit to something bigger going on with regards to the mineral system.
“It’s quite shallow with the shallowest mineralisation coming to within 5m of the surface and stems down to about 160 metres.
“It’s a breccia so it’s highly variable in grade and distribution of the resource box but we’ve been drilling with a lot more confidence knowing that high-grade parts of the deposit are very much part and parcel of the resource population.
“That’s the main reason we’ve been able to increase the grade and resource to contained ounces basically by infill drilling an area that had previously been drilled.”
On the subject of production, Anderson said that once the pre-feasibility had been completed he expected the company to move quickly onto full feasibility, but he felt it would be several years before the decision to mine was made.
In the meantime, optimisation studies are being conducted regarding high-grade starter pits, mineralised waste and the type of metallurgical options available to treat the ore.
“The choices we’re looking at came out of our original metallurgical work in 2013 which produced positive results in both leaching and flotation.
Standard leaching is the likely best option but we are also looking at flotation as an alternative to produce a concentrate we could possibly sell to a smelter.”
The soft host rock and shallow depth of the Paris deposit offers the potential for an open pit mining operation and H&SC has modelled and classified the Paris resource in accordance with this assumption.
“We’re a lot smaller than a project like Carrapateena but we’re at the surface and the Paris project is a very good fit for a company of our size, however we are aiming higher,” Anderson said.
“There’s potential for more silver, but more importantly larger copper-gold targets in the immediate Paris area.
“We believe the Nankivel prospect, just five kilometres south of Paris, is the start.
“We’ve located a large intrusive system, which is the centre to the whole mineral system, to which we think Paris is a satellite epithermal deposit and we see potential for other shallow epithermal deposits over the Nankivel area.
“We’re postulating that there’s porphyry copper-gold potential deeper under the epithermal outcrops.
Co-funded by the South Australian Plan for Accelerating Exploration (PACE) drilling initiative, results from Investigator’s first hole at Nankivel in August, 2016, strongly implied the hole was on the margin of a copper-gold mineralised porphyry system.
Four diamond drill holes were drilled in early 2017 aimed at Induce Polarisation chargeability anomalies within a large demagnetised zone.
All holes intersected potassic-altered porphyritic monzodiorite over the drilled area variously showing the fracturing, veining and multiple intrusives expected in a mineralised porphyry system.
The potassic alteration has the minerals expected in a mineralised porphyry – potash feldspar, biotite, magnetite and tourmaline.
The assays are pending, but the copper mineralisation is visually estimated to be low to modest in content and is not expected to produce significant grades.
The mineral zoning suggests that any higher-grade copper shell to a modelled late intrusive is at least 500m below the surface beneath current drilling.
Although deep, there is alteration and intrusive evidence for multiple porphyry events at Nankivel that implies shallower (telescoped) porphyry deposits.
The nearest town to the project is Kimba about 60km to the southeast with the Iron Road iron ore project to the west and the major town of Whyalla another 140km to the east.
Anderson said railway and port facilities were not a consideration as the company planned to produce silver dore that could be trucked quite easily.
A likely water source has been identified in a large palaeochannel aquifer 12km east of the Paris project through prior Investigator drilling and collaborative airborne electromagnetic surveying by CSIRO.
Investigator Resources Limited (ASX: IVR)
…The Short Story
18 King Street
Norwood SA 5067
Ph: +61 8 7325 2222
David Ransom, John Anderson, Bruce Foy, David Jones