Diamond explorer Newfield Resources (ASX: NWF) has announced an updated JORC-complaint resource estimate of more than 7.4 million carats across four identified kimberlites at its flagship Tongo project in eastern Sierra Leone.
Approximately 1.9 million carats – or 0.7 million tonnes, comprising 25% of the insitu resource – has been classified in the indicated category.
A recent mine development program over 10,792 metres of 50m infill core drilling produced the revised estimate across the project’s Kundu, Lando, Tongo Dyke-1 and Pandebu diamondiferous kimberlites.
Kundu is believed to contain an estimated 2.8m carats at a grade of 3.2 carats per tonne and a diamond value of US$194 per carat, while Lando contains 3.0m carats grading 2.9cpt at the same diamond value.
At Tongo Dyke-1, Newfield recorded 1.4m carats grading 1.5cpt at US$187/carat, while Pandebu’s resource contained 0.2m carats grading 1.1cpt at US$182/carat.
An additional seven kimberlites identified to date have not been included in the new resource estimate figures.
In total, the 11 kimberlites are contained within the project’s two adjacent mining licences covering a combined area of 134 square kilometres in the prolific diamond region.
Newfield executive director Mike Lynn said the revised estimate could be sign of things to come, with drilling to date limited to a depth of just 230m from surface.
“The diamond grades and values, in particular for Kundu and Lando, point to some of the most impressive kimberlites globally on a dollar per tonne rock value basis,” he said.
“Previous deeper drilling has shown these kimberlites extend to much greater depths which, along with the clear potential from other identified areas, would suggest [Tongo’s] global resource could be significantly increased in the future with more evaluation work.”
Data for 548 kimberlite samples collected at Kundu, Lando, Pandebu and Tongo Dyke-1 was taken from 332 drill core holes totalling 53,930m.
Areas above 135m of the kimberlites were drilled at 50m intervals along strike, while those below 135m were drilled at a density of generally 200m along strike.
Approximately 302 microdiamond samples totalling 1771 kilograms and yielding 8501 diamonds were used for grade modelling.
Another 10 bulk samples totalling 4052 tonnes and yielding 6304 carats of diamonds were used for grade and value modelling.
Using a composited specific gravity for each kimberlite, the total resource of 2.96mt was calculated to an approximate depth of 234m from surface for Kundu, Lando and Pandebu and 400m for Tongo Dyke-1.
“A number of drill holes intersected kimberlite below the current resource level, confirming continuity at depth and providing potential for an expanded resource in the future,” Mr Lynn said.
Meanwhile, front-end engineering design (FEED) for the Tongo development continues to progress towards targeted completion by year end.
Preliminary design work for the underground mine has been completed, based on a single portal at surface with two declines branching off to the adjacent Kundu and Lando kimberlites.
The mine design and geological block model – which will incorporate the updated grade and value estimates – will be the subject of mine optimisation studies.
Newfield expects this information will generate a production and revenue profile for the proposed mine from Kundu, Lando and Tongo Dyke-1 kimberlites, with Pandebu planned for incorporation into future mine planning.
Once the final design is agreed, the company will run a production optimisation schedule and establish capital and operating budgets.
Newfield is rapidly progressing the FEED stage with a view to accelerated development of the Tongo project in 2019.
At midday, shares in Newfield Resources were trading 41.67% higher at $0.170.