A new discovery of high-grade massive sulphide mineralization has been made beneath the existing Batu Mas JORC-compliant mineral resource area at Robust Resources’ Lakuwahi project on Romang Island. The new discovery and mineralized domain is called Batu Mas Deeps prospect and is of potentially very significant economic importance.
A diamond drill hole has intersected one of the most significant zones of mineralization yet to be encountered on Romang Island. It intersected a broad zone of polymetallic mineralization over 100 metres thick that contains a 6 metre zone of very high grade massive sulphides.
The intersections include 102.8 metres @ 5.71% combined base metals and 0.40 grams/tonne gold equivalent from 110 metres (0.19% copper, 2.54% lead, 2.99% zinc, 0.13 grams/tonne gold and 14 grams/tonne silver) including massive sulphides: 17 metres @ 25.67% combined base metals and 1.07 grams/tonne gold equivalent from 175 metres (0.86% copper, 11.97% lead, 12.84% zinc, 0.14 grams/tonne gold and 49 grams/tonne silver), including 6.0 metres @ 54.9% combined base metals and 1.78 grams/tonne gold equivalent from 176 metres (1.48% copper, 26.02% lead, 27.4% zinc, 0.16 grams/tonne gold and 49 grams/tonne silver).
The hole was terminated for technical reasons while still in strong mineralization so it is likely that the mineralization is even thicker than has been obtained in the drilling.
This mineralization is a down-dip extension of a mineralized zone in a previous hole completed two years ago. At the time this hole was recognized as having an intersection with significant potential but follow-up drilling was deferred while all available drilling resources were directed towards shallow oxide gold-silver targets.
The grades of the Batu Mas Deeps massive sulphide mineralization compare favourably with historical, current and proposed high-grade underground lead-zinc-silver and polymetallic deposits elsewhere, including the famous Broken Hill South underground mine in Australia which produced 34 million tonnes of ore grading 25.5% combined base metals and 230 grams/tonne silver to a depth of 1.7km before it closed in 1992, the Rosebery underground VMS mine in Tasmania which has been operating since 1893 and the undeveloped Anjing Hitam deposit in Sumatra, Indonesia.
The reason for this comparison is that if the Batu Mas Deeps exploration is successful in delineating even a modest tonnage at or near the grades obtained so far, then early development and extraction by underground mining of high-grade ore might be an option to enhance the economics of the Lakuwahi project as a whole.
Robust’s managing director Gary Lewis says, “Romang Island is now living up to its promise of becoming a world-class polymetallic deposit. The latest results are exceptional and appear to show a trend towards higher grade massive sulphides with increasing depth. Deeper drilling is now unlocking the full potential of Romang Island and Robust is committed to defining the full extent of the mineralization of Lakuwahi Caldera and other targets on the island.
“We are also committed to investigating the best way to exploit these exciting discoveries in order to produce an early cash flow. Depending on the results of further exploration, and if we can demonstrate that high-grade base metal ore can be mined and processed, this may prove to be an important pathway to early production.
“Also the high-grade manganese project is shaping up to be an important low-CAPEX stepping stone into cash flow and profitability, and advancing this project is a priority for Robust.”