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Arc Exploration Intersects Porphyry Copper-Gold At Trenggalek, East Java

Arc Exploration's (ASX: ARX) first exploration drill hole at its Trenggalek Project in East Java, Indonesia, has intersected extensive hydrothermal alteration and pyrite mineralisation, which is is positive for the share price today.

The hole is drilled as part of the joint venture with Anglo Americans (LON:AAL), which is providing funding while the company manages the exploration.

Evidence from Hole TRDD054 on the Jerambah Prospect, which was drilled to a final depth of 1,022 metres, suggests that it is located on the margins of an anticipated copper-gold system.

Jerambah is one of several new targets on the exploration tenement.

"The results from the hole confirm the presence of a large alteration system with traces of base metal mineralisation in a rock package that we believe is similar to that hosting the Tumpangpitu (Tujuh Bukit) porphyry copper-gold deposit further to the east," Arc managing director Dr Jeffrey Malaihollo said.

"The Jerambah prospect is large and needs more work to confirm the presence of a porphyry system. We are in the process of completing soil sampling and spectral analyses to help plan the forward program and will report on the progress of this work in the coming weeks."

Drilling Details

TRDD054 was an inclined diamond hole that tested a combined geological and geophysics target identified at Jerambah Prospect on the southern side of the Exploration IUP tenement.

The target is an extensive 2 kilometres by 1.5 kilometre silica-clay-pyrite alteration zone centred on igneous intrusions mapped at surface.

This coincides with discrete magnetic anomalies extending from a deeper seated stock-like body that were modelled from a 3D magnetics-inversion analysis of the airborne magnetics data.

The hole was completed at a final depth of 1022.3 metres and intersected a more than 800 metre thick package of propylitic, argillic/intermediate argillic, and advanced argillic-altered diatreme breccias, diorite, quartz diorite, andesite porphyry and quartz-feldspar porphyry, bedded volcaniclastic and calcareous sedimentary rocks.

These rock types and multiple overlapping alteration assemblages identified within them may be indicative of a porphyry-related system.

Disseminated pyrite mineralisation (<1-5%) occurs throughout the hole with locally traces of base metal sulphides.

This is reflected by the final assay results, which returned a few narrow (<2m wide) intercepts of up to 0.1% copper, 0.1 grams per tonne gold, 12 g/t silver and 88 ppm molybdenum (see Table 2).

The hole is interpreted to have intersected the weaker mineralised margins of a potential copper-gold system.

Soil sampling and spectral analyses over a large area that includes the Jerambah target are in progress and the results of these are awaited to help plan the forward drilling program.


The Trenggalek Project is an Exploration IUP tenement covering about 300square kilometres in the same arc segment that hosts the giant Tumpangpitu porphyry gold-copper deposit in the Southern Mountains of East Java.

The project has excellent infrastructure with a network of sealed to graded roads traversing almost all of the tenement area.

Jerambah is located about 2 kilometres southwest of the Buluroto epithermal gold-breccia prospect on the southern side of the Trenggalek tenement.

Previous drilling at Buluroto returned narrow epithermal gold intercepts that included 2 metres at 8.7 g/t gold in TRDD032.

Copper sulphide mineralisation in silicified breccia was intersected in another hole, TRDD025, returning a broad gold-copper-molybdenum intercept of 24.5m at 0.51g/t gold, 0.21% copper and 16 ppm Mo from 138.5 metres depth - providing indications of the deeper porphyry potential at Trenggalek.

The subsequent discovery of a large high-sulphidation epithermal alteration system centred on quartz-feldspar porphyry intrusions at Sumber Bening Prospect, located on the western side the Trenggalek tenement, provided further evidence for porphyry potential on the Trenggalek tenement.

Anglo American had elected in December 2012 to farm into Trenggalek.

It has the right to earn 51% interest in the project by sole funding US$ 10 million before 1 October 2016.

After spending US$ 10 million, Anglo American can move from 51% to 75% by sole funding an additional US$ 10 million.

On reaching 75%, Anglo American will free carry ARX for its remaining 20% through completion of a Pre-Feasibility Study.

PT. Sumber Mineral Nusantara holds the remaining 5% of Trenggalek.


The first hole in the drilling program appears to have been drilled on the margins of an anticipated copper-gold system.

Soil sampling and spectral analyses underway will help define the system, allowing the company to plan the forward exploration program.

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