WEST LOMBOK EXPLORATION ACTIVITIES
West Lombok has district-scale potential with drill-proven, high-grade, gold-rich copper porphyry and epithermal vein systems over three large prospects: Pelangan, Mencanggah and Selodong.
Southern Arc published the first resource estimate for the West Lombok property in July 2013, with an inferred resource totaling 1.49 million ounces of gold, 1.82 million ounces of silver and 397.3 million pounds of copper from three open-pittable epithermal gold deposits and one porphyry copper deposit. Further details are available in the press release and technical report.
Southern Arc entered into a joint venture in December 2014 to advance the project to small-scale gold production, with artisanal mining and processing of mineralization found from surface to 100 metres. Profits from the sale of gold and other minerals produced from these shallow mining activities will be split 25% Southern Arc, 65% PT GSE and 10% Local Government.
Southern Arc and PT GSE can continue to explore for deeper gold and porphyry targets on the property, when market sentiment warrants the expenditure. Should the partners choose to mine deeper targets on the property (deeper than 100 metres), profits will be split 65% Southern Arc, 25% PT GSE and 10% Local Government
Historical geological mapping and geochemical results within the West Lombok property confirmed the presence of anomalous gold, silver and base metals from low sulfidation epithermal and high sulfidation epithermal mineralized systems. Exploration by Newmont in the late 1980s and early 1990s within the West Lombok area noted that alteration lithocaps are commonly above mineralized intrusions or above known or untested porphyry gold-copper systems. The presence of both high sulfidation and low sulfidation vein outcrop, along with good prospectivity in the Pelangan and Mencanggah prospects, suggested that the West Lombok property has significant potential for hybrid high-low sulfidation systems or structurally controlled, high sulfidation copper-gold systems.
The company's exploration activities at West Lombok have been extensive. To date the Company has completed more than 40,000 m of drilling on the property, with up to 350 workers hired from the nearby communities at the peak of activity to construct drilling pads and access roads ahead of the drilling rigs while drilling was underway.
Pelangan Gold Prospect
Phase 1 drilling was completed at the Pelangan prospect in 2007, together with semi-detailed geological mapping and outcrop channel sampling of sub-parallel vein structures. A further 49 drill holes were completed at Pelangan between August 2011 and April 2012. Phase 2 drilling returned the best hole to date on the property with 17.4m @ 19.4 g/t gold. A total of 35 drill holes (6,642.70 metres) have been completed. Phase 2 drilling was focused on identifying and defining high-grade shoots within large continuous structures. The presence of such shoots are suggested by a high-grade quartz episode within the MSBs and increasing gold grade with depth. Phase 2 drilling confirmed high-grade events typical of epithermal boiling zones at both the Central Raja and Tanjung Lode structures and identified three high-grade shoots. Drill holes of significance include PLD040 (2.0m @ 5.84 g/t gold from 11.7m) and PLD043 (1.4m @ 9.3 g/t gold from 50.5m).
Phase 2 drilling at Pelangan Prospect (click for larger image)
Pelangan high-grade shoots (click for larger image)
Mencanggah Epithermal District
Concurrent with the drilling programs at Pelangan and Selodong, DGPS mapping and rock chip and channel sampling was initiated at Mencanggah in 2006. Sampling and geochemical mapping on the Mencanggah prospect identified Au-Ag epithermal quartz veining extending over a broad area of at least 6.5 km long by up to 4.5 km wide, including an aggregate proven strike length of more than 19 km. The broad area of silica ledges and acidic clay alteration at Mencanggah represents an incised lithocap to potentially significant porphyry style mineralisation.
Phase 1 drilling focused on the Bising and Waterfall targets, with 35 holes totalling 8,919.65 m. A total of 27 holes (totaling 6,633.95m) on a 100m x 100m grid basis were completed on the Waterfall target. Drilling tested outcrops of banded and brecciated epithermal chalcedonic-quartz veins for the presence of high-grade shoots at depth. The results confirm multiple vein zones at Waterfall, with highlight intersections of 4.75m @ 15.6 g/t gold and 15 g/t silver from 168.50m, including 2.0m @ 36.1 g/t gold and 31 g/t silver from 169.70m (MCG016) and 1.6m @ 11.0 g/t gold and 2.6 g/t silver from 122.35m (MCG006). The Company completed eight holes at Bising in 2011, located at 100 metre drill spacing to test the main Bising epithermal structural body, its extensions, and intersections with several crossing structures, identifying a 500-metre-long zone of mineralization. Highlight drilling intersections include 51.3m @ 1.5g/t gold from 35.6m (including 5.1m @ 3.5 g/t gold) and 39.0m @ 1.8 g/t gold from 34.0m (including 9.7m @ 4.9 g/t gold and 5.9 g/t silver). The extensive width of the main Bising epithermal body is inferred to result from the intersection of geological structures: a major west-northwest trending structure and several north-northwest trending structures, the latter of which form the dominant gold mineralized trend in the district.
Highlights from Mencanggah prospect (click for larger inmage)
Surface channel sampling along the extensive strike length at Bising returned high-grade intervals as well as very wide intervals of lower-grade gold mineralization. Channel sampling at Tibu Serai returned the highest grades on the property to date. Phase 2 drilling is currently underway, focused on infill drilling at Bising and, at Tibu Serai, testing down-dip from elevated rock-chip gold geochemistry in multiple veins that exhibit low silver-to-gold ratios. Low silver-to-gold ratios are a proven vector to higher gold grades in epithermal mineralization throughout the property.
Spectral analysis of surface rock alteration together with information gained from the drilling programs will also assist in the targeting of the inferred porphy mineralization below the advanced argillic lithocap in the Mencanggah prospect.
Selodong Intrusive Complex
At the southeastern end of the West Lombok property, Newmont and Southern Arc defined the 14 porphyry copper-gold targets that make up the Selodong Intrusive Complex with geochemistry, geophysics and alteration mapping. Subsequently, exploration activities focused on the Phase 1 deep diamond drilling program targeted the gold-rich copper porphyry prospects with over 17,800 m of diamond drilling. Significant intersections included 166.2 m @ 0.52% Cu and 0.85 g/t Au and 102.3 m @ 0.50% Cu and 1.05 g/t Au.
Phase 1 drilling at Selodong prospect (click for larger image)
In late 2011 Southern Arc flew a detailed, high-definition helicopter magnetic and radiometric survey over the property. A total of 2,590 line kilometres with north/south-oriented flight lines at 50m spacings were completed with the objective of defining both near-surface and buried copper-gold porphyry targets within the Selodong-Mencanngah-Pelangan mineralized structural corridor. The new geophysical data were modeled and interpreted by leading geophysical consultants using state-of-the-art processing methods and integrated with geological and geochemical databases to prioritize porphyry copper-gold target areas for the next phase of exploration. The resulting porphyry prospectivity study identified 17 porphyry targets on the property. Some of the targets had been previously tested in Phase 1 Selodong drilling and yielded significant Cu-Au porphyry mineralization, confirming the results of the prospectivity study. Two additional targets were drilled in early 2012.
West Lombok porphyry prospectivity study (click for larger image)
To date 32 drill holes have been completed on porphyry targets at Selodong for a total of 18,833.3 m.
Latest News Releases
November 14, 2017
Southern Arc Announces Additional Investment in Tethyan
October 31, 2017
Southern Arc Year-end Financial Results
September 5, 2017
Southern Arc Agrees to Sell West Lombok Property