Arc Exploration reports Indonesian mining ops
Thursday, October 17 2013 - 05:59 AM WIB
ARX is exploring for gold and base metal deposits along Indonesia ?s highly prospective magmatic arcs and associated geological terranes. The primary exploration targets are porphyry-related copper-gold and high-grade epithermal gold-silver veins.
Trenggalek Project, East Java (95% ARX)
ARX has a joint venture with PT. Sumber Mineral Nusantara (?SMN?), an Indonesian company which holds the Trenggalek Exploration IUP tenement that covers an area of approximately 300 km2 in the Southern Mountains of East Java.
In December 2012, ARX announced that Anglo American had elected to enter into an agreement with ARX and SMN to farm into the Trenggalek Project. Details of this agreement were presented in the December 2012 quarterly report. Formal legal documentation in support of the Joint Venture between ARX and Anglo American was signed on 22 August 2013 . Exploration activities at Trenggalek are currently managed by ARX but fully funded by Anglo American.
An extension to the Pinjam-Pakai (?Borrow Use?) Forestry Permit for the Trenggalek IUP was granted by the Indonesian Ministry of Forestry and is valid until the 3 November 2015 . This allows the company to conduct exploration work on several targets in production forestry areas within the tenement.
Targets
The focus of early exploration work by ARX on the tenement was on gold. Several shallow intermediate-sulphidation epithermal quartz vein systems associated with hydrothermal breccias and silica cappings in volcanic rocks and limestones were identified and had limited drill testing.
An exciting new phase of porphyry copper-gold exploration commenced in late-2011 following the discovery of a high-sulphidation epithermal alteration system at Sumber Bening. Other similar alteration systems have since been identified in the project area and these could be linked to porphyry gold-copper targets at depth.
Potential for major porphyry copper-gold deposits in the region is highlighted by the discovery of the Tumpangpitu deposit in the Tujuh Bukit district, located some 200 km to the east of Trenggalek. Tumpangpitu is in the same belt of rocks hosting the giant Batu Hijau and Elang copper-gold deposits on Sumbawa within the Sunda-Banda magmatic arc. Trenggalek contains a similar package of rocks to those hosting these three major porphyry deposits.
The Joint Venture with Anglo American announced in 2012 provides an opportunity to test the porphyry potential of the Trenggalek tenement.
Sumber Bening Prospect
This prospect lies on prominent north-northwest-trending structures that cut across a 4km diameter-circular feature on the western side of the IUP. It contains an extensive area (+3 km x 2 km) of silica-pyrophyllite-dickite-pyrite alteration with localised vughy silica alteration centred on volcaniclastic rocks and quartz-feldspar porphyry intrusions. Earlier reported rock chip sampling has returned up to up to 0.14 g/t gold and anomalous porphyry-pathfinder metals that include bismuth (up to 1410 ppm Bi), copper (up to 277 ppm Cu) and molybdenum (up to 37 ppm Mo).
Modelling and interpretation of airborne magnetics & radiometrics and ground 3DIP geophysical data collected over this prospect in the preceding 18 months was completed by a geophysical consultant.
His work concluded that good potential exists for a porphyry copper-gold system beneath the high-sulphidation alteration lithocap at Sumber Bening.
The geophysical data at Sumber Bening support the presence of widespread pervasive alteration centred on quartz-feldspar porphyry intrusions at surface. Geophysical signatures suggest that the near-surface high-sulphidation alteration lithocap extends at depth and may grade into zones of secondary (replacement) magnetite-rich potassic alteration and structures associated with porphyry emplacement and copper-gold mineralization.
Drilling at Sumber Bening is planned upon completion of socialization of the work program to the local community.
Target Generation
Multiple targets regarded as having potential for buried porphyry copper-gold systems were derived from an initial 2D interpretation done on the 2012 airborne magnetics and radiometrics survey, and reported in the March 2013 Quarterly Report.
One of these targets, a 5 km x 6 km block area surrounding the Buluroto Prospect in the southeast corner of the Trenggalek IUP, was assessed by 3D magnetics-inversion modelling by Chris Moore of Moore Geophysics (Melbourne).
Buluroto contains an intermediate-sulphidation epithermal gold vein-breccia target that was tested by shallow scout drilling in 2010 and returned a gold-copper-molybdenum intercept of 24.5m at 0.51 g/t Au, 0.21% Cu & 16 ppm Mo from 138.5m down-hole from chalcopyrite-bearing breccia in TRDD025. This intercept was one of the first indications of the deeper porphyry potential at Trenggalek.
The aim of the 3D magnetics inversion modelling work was to identify geophysical signatures that might indicate the presence of mineralized porphyry systems and to aid with generating drill targets. The main conclusions of the study were:
- The Buluroto block area covers a large annular magnetics response containing discrete high frequency magnetic features and interpreted zones of alteration (demagnetisation).
- A large, vertical, contiguous body, oblong in plan section, was modelled to extend from >5000m depth to within 500m of surface. This is interpreted as an intrusive sub-volcanic ?stock? within a volcanic-intrusive complex that is about of about 2.5km in diameter and is similar in size to that hosting the giant Tumpangpitu porphyry copper-gold deposit at Tujuh Bukit.
- Several intrusive apophyses extend upward from this stock to within a few hundred meters of surface. These are considered prospective for porphyry style mineralization - particularly where a physical connection between the apophysis and main intrusive indicates a possible syngenetic origin and provides a pathway for fluid transport.
- The main sub-volcanic intrusive is cut by large WNE- to NW-trending crustal structures and it is possible that intrusions and porphyry-related mineralising fluids exploited these structures.
There were thirteen discrete targets identified within the Buluroto block area for follow up ground evaluation. These targets were derived from features interpreted from the 3D magnetics-inversion analysis; including magnetic or non-magnetic structural lineaments interacting with inferred alteration zones centred on or around intrusive apophyses/plugs connected to the deeper stock-like intrusion.
Follow-up field evaluation of the 13 targets was completed. Two areas of extensive silica-clay-pyrite alteration were identified within Targets 9 and 11. The other targets contain relatively minor occurrences of alteration and veining within largely unaltered volcanic rocks.
The two large alteration zones found within Target 9 (Buluroto North) and Target 11 (Jerambah) are each centred on quartz diorite or Quartz Feldspar Porphyry (QFP) intrusions and measure at least 1.5km x 1km and 2km x 1.5km, respectively. The dominant clay minerals within these alteration zones were determined by Terraspec analyses and include dickite, pyrophyllite and illitic clays. Vughy silicification and quartz stockworks locally occur within these large alteration footprints. The silica-clay-pyrite alteration overprints an earlier patchy propylitic alteration assemblage of chlorite-epidote-magnetite in the intrusions and volcanic rocks.
Initial rock chip grab sampling of altered outcrops within the respective target areas returned up to 1.75 g/t Au and 93 ppm Cu in Target 9 (Buluroto North) and up to 562 ppm copper and 37 ppm molybdenum in Target 11 (Jerambah). Grid-based soil geochemical sampling is planned over both target areas.
The occurrence of higher temperature acid clays (dickite & pyrophyllite) suggests the possibility of high-sulphidation alteration lithocaps within both target areas. The large size of the alteration footprints and association with discrete quartz-diorite/QFP intrusions, as well as indications of gold-copper-molybdenum anomalism in rock chip, are highly encouraging and support the potential for mineralized porphyry systems at depth.
Start of Drilling
Results from the follow-up field evaluation were sufficiently encouraging to plan an initial scout drill hole on Target 11 (Jerambah Prospect).
Drilling commenced in the first week of October following socialization of the work program to the local community. Drilling is contracted to PT. Maxidrill Indonesia using a MXD-420 man-portable diamond drill rig with a depth capacity of up to 650 metres in PQ-HQ-NQ core sizes.
The first hole (TRDD054) at Jerambah Prospect is located about 2 km southwest of the Buluroto epithermal gold-breccia prospect. This hole tests a magnetic target delineated beneath the +2.5 km x 1 km alteration zone centred on a quartz diorite/QFP intrusion. The magnetic target is interpreted to be possibly secondary magnetite associated with potassic alteration and the top of which is predicted to be below 400 metres depth down-hole.
The hole is part of a larger program that will test a number of geophysical targets identified on the Trenggalek IUP.
Exploration expenditure at Trenggalek for the quarter totalled US$364,943 and this was wholly funded by Anglo American.
Strategic Alliance with Anglo American in Papua
The Company holds a 20% interest in a Strategic Alliance with Anglo American and Indonesian parties to explore for copper-gold deposits in Papua and West Papua provinces.
Anglo American is responsible for managing and funding all exploration activities in Papua.
The Alliance currently holds three Exploration IUP tenements owned by Indonesian parties pursuant to the Strategic Alliance. These cover nearly 3,000 km2 at the centre of the Bird?s Head peninsula in West Papua Province which cover prospective ground in the same region that hosts Grasberg - Indonesia?s largest porphyry copper-gold deposit. (end of edited excerpt)