After months of mapping, sampling and geophysical surveys, Estrella Resources has finally cranked up a reverse circulation (RC) diamond drill rig at its massive and previously untested Laleno Dome copper-gold prospect on the far eastern tip of Timor-Leste. The project resides entirely within the Lautem Municipality, the country's easternmost administrative district.
The initial 2650-metre RC program marks the first time a drill bit has ever directly tested the expansive, roughly 10-kilometre-wide dome structure.
The shallow drilling will probe a suite of compelling targets, including near-surface porphyry outcrop, conductivity anomalies identified by previous surveys and a possible manganese-bearing horizon. The company says it expects to complete the campaign by mid-December, subject to operating conditions.
Laleno Dome is a significant geological structure that rises some 700m above the surrounding terrain. Estrella's surface work has already painted an encouraging picture, with copper occurrences identified at nine separate locations along a 12km section of the dome’s margin.
Previous surface sampling has yielded assays of 0.66 per cent copper and 0.53 per cent copper from porphyritic intrusive rocks, lending weight to management’s porphyry exploration model. More impressively, selected rock-chip samples also returned stunning grades of up to 60.34 per cent copper and 1.3 grams per tonne (g/t) gold.
Petrographic studies of the rock samples have also bolstered the prospect's geological case, identifying hydrothermally altered porphyritic diorite and microdiorite rocks with quartz-carbonate veinlets, silica alteration and disseminated pyrite – all classic calling cards of a porphyry-style mineral system.
Adding another layer of exploration intrigue, a recent Mobile MT geophysical survey lit up high-conductivity anomalies, including some the company has interpreted as conductive “plumes” extending upwards from depth on the flank of the dome. While conductivity may have several geological causes, one of the more exciting possibilities is that it represents sulphide mineralisation, a typical host for many major copper-gold deposits.
Estrella Resources managing director Robert Mencel said: “Commencing drilling at Laleno Dome moves us from interpreting surface samples and geophysical anomalies to testing the geology beneath the prospect. The first phase will investigate shallow targets, including near-surface porphyry outcrop and a possible manganese-bearing horizon.”
While the current RC campaign is focused on shallow targets, Estrella is already drawing up plans for a more ambitious second phase of work. The company is designing three deeper holes, each planned to reach 500m, using a 100m RC drill hole pre-collar, followed by a 400m diamond core tail.
The deeper program, which remains subject to government approval, is intended to test the conductive anomalies at depth and determine whether they are associated with sulphide-bearing mineralisation.
For a prospect of this scale, with compelling surface geochemistry and intriguing geophysical targets, it is remarkable that Laleno Dome has remained untested by drilling until now.
Away from Laleno Dome, Estrella is making commercial headway across its broader Timor-Leste portfolio. The company has signed a binding sales agreement with Australian private company Repusource Pty Ltd for 27,000 tonnes of manganese ore from its Ira Miri project. The manganese venture is operated through the Estrella Murak Rai joint venture, in which Estrella holds 70 per cent.
Meanwhile, the company has also kicked off a scoping study at its Werumata limestone project, following the definition of a substantial 621-million-tonne inferred resource and is planning a 4000-metre drilling campaign at the nearby high-grade Sagadate limestone project, subject to regulatory approval.
As its first RC hole now probes the depths of the Laleno Dome, Estrella has moved beyond interpreting the geological signals at surface to directly looking at what might be causing them at depth. With a busy drilling schedule planned ahead of the new year, the company may not have long to wait for some answers.
Is your ASX-listed company doing something interesting? Contact: matt.birney@businessnews.com.au
